Electrical System

Electrical System
Electrical System
Electrical System
Section 8A - Electrical System
Table of Contents
Finding Other Diagrams...................................8A-2
General Information.........................................8A-2
Precautions......................................................8A-2
Industry Standards and Regulations................8A-3
Battery and Battery Cables Requirements.......8A-4
Battery .....................................................8A-4
Battery Cables..........................................8A-5
Electrical Connections.....................................8A-6
SmartCraft Product...................................8A-6
Engine Harness........................................8A-6
Engine Connections..................................8A-9
Continuity Wire Connection......................8A-9
Accessories............................................8A-11
Audio Warning System..................................8A-11
Audio Warning System without Emissions
Control....................................................8A-11
Audio Warning System with Emissions
Control....................................................8A-11
Multiple EFI Engine Battery Precautions.......8A-13
Situation..................................................8A-13
Recommendations..................................8A-13
Battery Switch................................................8A-14
Finding Other Diagrams.................................8A-14
Power Harness..............................................8A-14
Battery Isolator...............................................8A-15
Battery Isolator Diagram.........................8A-16
8
A
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Page 8A-1
Electrical System
Lubricant, Sealant, Adhesives
Tube Ref No.
25
Description
Liquid Neoprene
Where Used
Part No.
All electrical connections except the battery
92- 25711 3
Finding Other Diagrams
NOTICE
Refer to the appropriate Mercury MerCruiser Diagram Binder for wiring diagrams or other diagrams not found
in this manual.
General Information
This section covers the engine portion of the electrical system. For instrumentation related
information, see Section 9.
The electrical system is a 12‑volt, negative ground system. High output (65/72 amp)
alternators are included as standard equipment. Their high output design helps ensure that
the battery remains fully charged for trouble‑free starting, while providing extra capacity to
handle the accessories used on today's boats. All alternators are equipped with an external
sensing circuit to maintain the battery at the optimum voltage level, while providing for the
use of a battery isolator, if desired. Special high‑capacity marine starters are also employed
to provide reliable starting and long life in the rigorous marine environment. Mercury
MerCruiser starters, alternators, distributors, solenoids, circuit breakers, fuses, and other
components that could generate a spark comply with external ignition standards and
regulations to prevent the ignition of combustible fumes in the engine compartment should
they exist. These components should not be confused with standard automotive
components, which typically do not have this provision. The electrical system is equipped
with numerous overcurrent protection devices (circuit breakers, fuses) to protect the engine
against shorts and overloads. See Wiring Diagrams for the location of these devices. The
engine compartment should be designed to allow access to these components.
IMPORTANT: No one component is more important in ensuring the reliability of the
electrical system than is the battery and related hardware. The installation of the battery
and cables is the responsibility of the boat manufacturer. The guidelines outlined in this
section must be carefully followed when selecting and installing these items.
Precautions
! WARNING
Avoid fire or explosion hazard. Electrical, ignition, and fuel system components on
Mercury Marine products comply with federal and international standards to minimize risk
of fire or explosion. Do not use replacement electrical or fuel system components that do
not comply with these standards. When servicing the electrical and fuel systems, properly
install and tighten all components.
! WARNING
Performing service or maintenance without first disconnecting the battery can cause
product damage, personal injury, or death due to fire, explosion, electrical shock, or
unexpected engine starting. Always disconnect the battery cables from the battery before
maintaining, servicing, installing, or removing engine or drive components.
Page 8A-2
90-863758070 APRIL 2008
Electrical System
! CAUTION
Failure to protect wiring with an appropriate fuse can damage the wiring and start a fire.
When installing any accesories, we recommend using a Mercury accessory kit. Always
use the appropriate fuse to protect wiring.
IMPORTANT: Refer to the following precautions when working on or around the electrical
harness, or when adding other electrical accessories, to avoid damage to the electrical
system.
• Do not tap accessories into the engine harness.
• Do not puncture wires for testing (probing).
• Do not reverse the battery leads.
• Do not splice wires into the harness.
• Do not attempt diagnostics without the proper, approved service tools.
IMPORTANT: The accessory wire in the 14‑pin harness will not support amperage in
excess of 15 amps. Refer to Quicksilver Accessories for an optional relay kit that will
accommodate a higher amperage draw.
Industry Standards and Regulations
! WARNING
Improper design and installation of the electrical system can result in serious injury or
death. Adhere to all applicable marine regulations (United States Coast Guard [USCG],
European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards they
reference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers
[SAE], International Standards Organization [ISO], etc.) for the market in which the boat
will be sold.
The following excerpts from the ABYC Standards should be observed when designing and
installing the electrical system. These are just a few of the more fundamental standards
that, if observed, can significantly improve the overall reliability and durability of the boat
and engine package. The list is not intended to be all‑inclusive, and should not be used as
a substitute for reading the standards.
• Current carrying conductors shall be routed as high as practical above bilge water level
and other areas where the water may accumulate. The wiring and connections must
be water‑tight.
• Conductors should be routed as far away as practical from exhaust pipes and other
heat sources. Unless an equivalent thermal barrier is provided, a clearance of 51 mm
(2 in.) should be provided between conductors and the water cooled Mercury
MerCruiser exhaust system components.
• Conductors that may be exposed to physical damage shall be protected by self‑draining
loom, conduit, tape, raceways, or other equivalent protection.
• Conductors passing through bulkheads or structural members shall be protected to
avoid insulation damage such as chafing by using grommets.
• Conductors should be routed to clear sources of chafing such as steering cable and
linkages, throttle connections, and other moving engine components.
• Conductors should be supported throughout their length and should be secured at least
every 46 cm (18 in.), using industry approved fasteners.
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Electrical System
•
•
•
•
•
•
•
All connections shall be in locations protected from the weather, in weatherproof
enclosures or should be watertight. If connections are exposed to immersion, they must
be watertight.
Metals used for terminal studs, nuts, and washers shall be corrosion resistant and
galvanically compatible with the conductor and terminal lug. Aluminum and unplated
steel shall not be used for studs, nuts, and washers.
No more than 4 conductors shall be secured to any one terminal stud.
Only industry approved terminals shall be used, which typically include ring and captive
spade types.
Solder shall not be used as the sole means of mechanical connection in any circuit.
Solder connections shall be properly supported to minimize flexing of the solder
connection.
Twist‑on connectors (i.e. wire nuts) shall not be used.
Wire size and insulation rating shall be selected in accordance with industry standards
with the proper overcurrent protection being used.
Battery and Battery Cables Requirements
NOTICE
Reversing the battery cables can damage the electrical system. Connect the positive lead
to the positive terminal and the negative lead to the negative terminal.
! WARNING
Improper design and installation of the electrical system can result in serious injury or
death. Adhere to all applicable marine regulations (United States Coast Guard [USCG],
European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards they
reference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers
[SAE], International Standards Organization [ISO], etc.) for the market in which the boat
will be sold.
! CAUTION
Disconnecting or connecting the battery cables in the incorrect order can cause injury
from electrical shock or can damage the electrical system. Always disconnect the
negative (‑) battery cable first and connect it last.
Battery
IMPORTANT: Follow all applicable regulations or industry standards when installing the
battery. Ensure that the battery cable is installed so that it meets the pull test requirements
and that positive battery terminal is properly insulated.
IMPORTANT: Some areas require that the battery be installed in an enclosed case. Refer
to regulations for your area.
IMPORTANT: Always tighten battery cables with a wrench.
Select a battery that meets these specifications:
Use a 12‑volt marine type battery with tapered post or side‑terminal connectors. Don not
use a battery with wing nut connectors. Ensure that the battery capacity rating meets or
exceeds the recommended cranking battery specifications.
Cranking Battery Specifications
Model
Page 8A-4
Minimum required rating
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Electrical System
All carburated models
375 cca / 475 mca / 90 Ah
All MPI models
750 cca / 950 mca / 180 Ah
All DTS Models
800 cca / 1000 mca / 190 Ah
Ensure that the battery has a reserve capacity rating that meets or exceeds the electrical
accessory loads of the particular application. Refer to applicable standards for calculation
procedure.
• Install the battery according to the following specifications:
• As close to the engine as possible.
• In an accessible location for service.
• Ensure that the battery compartment is properly vented in accordance with the industry
standards and regulations.
• Ensure that the battery is not installed above or below a fuel tank, fuel filter, or fitting
in a fuel line.
• Ensure that the battery is installed so that the metallic objects cannot come in contact
with the ungrounded (positive) battery terminal.
• Ensure that the fuel system components within 30.5 cm (12 in.) and above the
horizontal plane of the battery top surface are shielded with dielectric material.
• Ensure that the battery parts that are continuously energized, such as the positive
battery terminal and the cable connections are physically protected with boots or other
forms of protection to prevent accidental short circuits.
• Ensure that the battery cable connections are tight and protected with a battery
connection sealant.
• The battery installation for multiple engine installations require special battery
considerations.
Battery Cables
IMPORTANT: Battery cables must comply with SAE J1127 or comparable standards.
• Select proper size positive (+) and negative (‑) battery cables using the chart.
Battery Cable Length Requirements
Average Cable Length
Cable Gauge
Up to 1.1 m (3‑1/2 ft.)
25 mm2 (4)
1.1–1.8 m (3‑1/2–6 ft.)
35 mm2 (2)
1.8–2.3 m (6–7‑1/2 ft.)
50 mm2 (1)
2.3–2.9 m (7‑1/2–9‑1/2 ft.)
50 mm2 (0)
2.9–3.7 m (9‑1/2–12 ft.)
70 mm2 (00)
3.7–4.6 m (12–15 ft.)
95 mm2 (000)
4.6–5.8 m (15–19 ft.)
120 mm2 (0000)
Refer to the following battery cable guidlines:
• Multiple engine installations (including generator sets) require that a negative cable be
run between the engines. The cable must be of sufficient size to carry the highest
cranking current that could be encountered.
• On applications with crossover (parallel) cranking motor circuits in multiple engine
installations (including generator sets), a separate negative ground cable must be run
between the engines (in addition to the cable mentioned above). The cable must be
sized to handle the highest possible load in the cranking circuit.
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Electrical System
•
•
•
•
•
•
Battery cables must be routed above normal bilge water levels throughout their length.
Battery cables must be routed to avoid contact with metallic fuel system components.
The positive battery cable must be routed to avoid contact with any portion of the engine
or drive train.
Cables that are exposed to physical damage should be protected by conduit, raceways,
tape, etc.
Cables that pass through bulkheads or other structural members should be protected
against chafing with grommets, etc.
To ensure good electrical contact, use only electrical grade (resin flux) solder when
soldering battery cable terminals to cable ends. Some form of mechanical connection
(for example, by swaging or crimping) is also recommended, and is required if length
of solder connection is less than 1‑1/2 times the diameter of the stranded area of the
cable. See Multiple EFI Engine Battery Precautions.
Electrical Connections
Refer to the following precautions when working on or around the electrical harness, or
when adding other electrical accessories, to avoid damage to the electrical system.
• Do not tap accessories into the engine harness.
• Do not puncture wires for testing (probing).
• Do not reverse the battery leads.
• Do not splice wires into the harness.
• Do not attempt diagnostics without the proper, approved service tools.
IMPORTANT: When routing all wire harnesses and hoses, ensure that they are routed and
secured to avoid potential contact with moving parts hot spots on the engine.
Tube Ref No.
25
Description
Liquid Neoprene
Where Used
Part No.
All electrical connections except
the battery
92- 25711 3
SmartCraft Product
A Mercury SmartCraft System instrument package can be purchased for this product. A
few of the functions the instrument package will display are engine RPM, coolant
temperature, water pressure, battery voltage, fuel consumption, and engine operating
hours.
The SmartCraft Instrument package also aids in Engine Guardian diagnostics, by
displaying critical engine alarm data and indicating potential problems.
Refer to the Mercury SmartCraft Operator's Supplement for the warning functions and
basic operation of the SmartCraft instrument package. Refer to the instructions included
with the instruments for installation instructions.
Engine Harness
GENERAL INFORMATION
Fuel injected MerCruiser engine models are SmartCraft ready and may be rigged using
the SmartCraft instrumentation, analog instrumentation, or a combination of the two.
If using anadapter, do not overtighten the clamp or deform the connector. Ensure that the
connection is oriented at angle or installed in a location that places the connection at risk
for exposure to moisture. Mount the connector with a downward slope of 30º from horizontal
to provide additional protection from water intrusion. Ensure that the location does not
interfere with moving parts on the engine or boat.
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Electrical System
The adpater limits accessory current through the boat harness to 15 amps, even if the boat
has a 10‑pin harness that is capable of handling larger accessory loads.
SmartCraft data is carried in the 14‑pin system without the use of a special data harness.
SmartCraft data is not supported across the adapters. A separate CAN line will be needed
on a boat using SmartCraft instrumentation and an adapter harness.
ENGINE HARNESS INSTALLATION
! CAUTION
Failure to protect wiring with an appropriate fuse can damage the wiring and start a fire.
When installing any accesories, we recommend using a Mercury accessory kit. Always
use the appropriate fuse to protect wiring.
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Electrical System
IMPORTANT: The accessory wire in the 14‑pin harness will not support more than 15
amps. The main power relay fuse may blow if an excess of 15 amps is applied. Refer to the
Mercury Precision Parts Accessories Guide for an optional accessory power relay kit
that will accommodate higher amperage draw.
1. Route the instrumentation wiring harness back to the engine, making sure that the
harness does not rub or get pinched. If an extension harness is required, be sure to
secure the connection properly.
2. Fasten the harnesses to the boat at least every 45.7 cm (18 in.) , using appropriate
fasteners.
3. Models with a 10‑pin harness, connect the instrumentation wiring harness to the engine
harness plug. Secure the connection with the hose clamp.
4. Tighten the hose clamp to secure the wiring harness to the engine harness plug.
5. Models with a 14‑pin harness, connect the instrumentation wiring harness to the engine
harness plug.
a. Connect the depth transducer connector to the DLC/Depth transducer connector
on the engine harness.
b. Connect the paddle wheel/tank level connector.
c. Connect the power harness (Clean Power with 5‑amp fuse) connector (DTS and
PCM09 only).
a
d
c
b
e
12118
Typical 14‑pin DTS harness
a - Engine harness connector
d - DLc/depth transducer connector
b - Transmission harness connector
e - Power harness connector/clean
power with 5‑amp fuse (DTS and
c - Paddle wheel/tank level connector
PCM09 only)
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90-863758070 APRIL 2008
Electrical System
Engine Connections
b
a
c
23629
a - Starter solenoid
b - 90‑amp fuse
c - Positive (+) battery cable
NOTE: The negative (‑) battery wire can be connected to the port or starboard flywheel
housing ground stud.
a
20459
a - Negative (–) battery wire
Continuity Wire Connection
IMPORTANT: Do not attach any accessory ground (–) wires to the transom plate ground
point. Accessory ground wires can only be attached to the ground stud on the engine.
IMPORTANT: Models equipped with a 14‑pin engine wiring harness are equipped with a
separate transom harness. Incorporated into the transom harness is a continuity circuit
ground lead. Proper ground connection between the transom and the engine is required
to ensure proper operation of the corrosion protection system.
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Electrical System
1. For models equipped with a 14‑pin engine harness, secure the transom harness
continuity circuit ground lead to the inner transom plate using the grounding screw on
the upper port side of the inner transom plate. Tighten the screw securely.
a
b
c
23598
a - Transom harness ground lead
b - Grounding screw
c - Inner transom plate
2. If the transom plate has a continuity wire attached, it can be removed or attached to
the flywheel housing. Whether or not this additional continuity wire is used, the
continuity wire in the transom harness must be connected to the continuity circuit at the
transom plate.
! WARNING
Excessive current load in the continuity wire may cause the potential for fire, leading to
injury or property damage. Do not connect the negative (‑) battery cable to the transom
assembly.
IMPORTANT: Ensure that the continuity wire is connected between the engine and the
inner transom plate. This lead is critical for the corrosion protection system to operate
properly, especially when the MerCathode is being used.
• Do not connect the negative cable to other than the unpainted locations shown to
ensure good electrical contact.
NOTICE
An improperly secured positive (+) battery cable or accessory lead can stress starter
terminals or damage the starter solenoid. Secure accessory leads and the positive battery
cable to the boat.
•
•
•
Page 8A-10
Secure cables to the boat using industry‑approved fasteners to prevent stressing the
cable and terminals.
Connections at the engine should be coated with liquid neoprene to prevent corrosion.
Battery connections should be coated with battery connection sealant to help retard
corrosion.
90-863758070 APRIL 2008
Electrical System
Accessories
! WARNING
Improper design and installation of the electrical system can result in serious injury or
death. Adhere to all applicable marine regulations (United States Coast Guard [USCG],
European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards they
reference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers
[SAE], International Standards Organization [ISO], etc.) for the market in which the boat
will be sold.
•
Coat connections with liquid neoprene to prevent corrosion.
NOTICE
An improperly secured positive (+) battery cable or accessory lead can stress starter
terminals or damage the starter solenoid. Secure accessory leads and the positive battery
cable to the boat.
•
•
Secure leads to the boat using industry‑approved fasteners to prevent stressing the
leads and starter terminal.
Refer to industry standards and regulations for additional information.
Audio Warning System
Audio Warning System without Emissions Control
1. Place the large decal on the instrument panel, or another location where the operato
can see it easily.
ALARM INDICATES LOW
OIL OR OVERHEATING
a
APPLY THE PROPER DECAL TO THE DASHBOARD
OR OTHER APPROPRIATE LOCATION:
b
AUDIO WARNING HORN WILL SOUND WHEN:
1. ENGINE OIL PRESSURE IS TOO LOW
2. ENGINE TEMP. IS TOO HIGH, OR
3. DRIVE OIL LEVEL IS TOO LOW
TO TEST AUDIO WARNING HORN:
TURN KEY TO "ON" POSITION (ENGINE OFF)
7799
a - Small decal (transparent)
b - Large decal
2. Test audio warning system during pre‑delivery preparation section.
Audio Warning System with Emissions Control
IMPORTANT: The audio warning system will indicate that a problem has occured. It does
not protect the engine from damage.
Your Mercury MerCruiser power package may be equipped with an audio warning system.
Most faults cause the warning horn circuit to activate. How the warning horn activates
depends on the severity of the problem.
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Electrical System
There are three warning horn states:
• Caution
• Severe
• Onboard Diagnostic Marine (OBDM) fault
CAUTION
If a caution is detected, the audio warning system will sound for six one‑second intervals.
ON
a
1
ON
ON
ON
ON
ON
1
1
1
1
1
1
1
1
1
1
OFF
OFF
OFF
OFF
OFF
OFF
b
33402
a - Horn (on or off)
b - Time (in seconds)
Below are some examples of a caution fault:
• Transmission fluid temperature is too hot
• Drive oil is low
• Sensor failure
SEVERE
IMPORTANT: If you experience a severe fault, contact your authorized Mercury
MerCruiser dealer.
If a severe fault is detected, the audio warning system will sound for six seconds, turn off
for six seconds, then sound for six more seconds.
ON
a
6
ON
6
6
OFF
b
33403
a - Horn (on or off)
b - Time (in seconds)
The following are examples of conditions that could trigger a sever fault:
• Engine oil pressure is too low
• Engine temperature is too hot
• Seawater pressure is too low
• Transmission pressure is low
Page 8A-12
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Electrical System
OBDM
If an OBDM fault is detected, the audio warning system will sound for one five‑second
interval, followed by a, 1/2‑second interval every 60 seconds for certain faults related to
the emissions or fuel system. See your authorized Mercury MerCruiser dealer for
assistance.
ON
a
5
ON
60
OFF
ON
60
½
b
OFF
½
ON
60
½
OFF
33404
a - Horn (on or off)
b - Time (in seconds)
TESTING THE AUDIO WARNING SYSTEM
1. Turn the ignition switch to the "ON" position without cranking the engine.
2. Listen for the audio alarm. The alarm will sound if the system is functioning correctly.
Multiple EFI Engine Battery Precautions
Situation
Alternators: Alternators are designed to charge the battery that supplies electrical power
to the engine that the alternator is mounted on. When batteries for two different engines
are connected, one alternator will supply all of the charging current for both batteries.
Normally, the other engine's alternator will not be required to supply any charging current.
EFI Electronic Control Module (ECM): The ECM requires a stable voltage source. During
multiple engine operation, an onboard electrical device may cause a sudden drain of
voltage at the engine's battery. The voltage may go below the ECM's minimum required
voltage. Also, the alternator on the other engine may now start charging. This could cause
a voltage spike in the engine's electrical system.
In either case, the ECM could shut off. When the voltage returns to the range that the ECM
requires, the ECM will reset itself. The engine will now run normally. This ECM shut down
usually happens so fast that the engine just appears to have an ignition miss.
Recommendations
Batteries: Boats with multi‑engine EFI power packages require each engine be connected
to its own battery. This ensures that the engine's electronic control module (ECM) has a
stable voltage source.
Battery Switches: Battery switches should always be positioned so each engine is running
off its own battery. DO NOT operate engines with switches in BOTH or ALL position. In an
emergency, another engine's battery can be used to start an engine with a dead battery.
Battery Isolators: Isolators can be used to charge an auxiliary battery used for powering
accessories in the boat. They should not be used to charge the battery of another engine
in the boat unless the type of isolator is specifically designed for this purpose.
NOTE: Sure Power Industries Inc., Model 32023A meets this design specification.
1. The boat may have 2 engines connected to a single Model 32023A battery isolator.
2. The Model 32023A battery isolator is connected to 2 banks of batteries.
3. Each bank contains 2 batteries with the cranking battery for 1 engine in each bank.
4. The second battery in each bank is connected in parallel to the cranking battery.
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Page 8A-13
Electrical System
5. The Model 32023A battery isolator is designed for this type of use; 2 battery banks, 2
charging sources, 120 amps (maximum alternator output).
6. When the engines are running, either engine's alternator could be charging either bank
of batteries through the Model 32023A battery isolator.
Any other manufacturer's battery isolator that is the same type as the Sure Power Inc.,
Model 32023A could also be used.
Generators: The generator's battery should be considered another engine's battery.
Battery Switch
! WARNING
Improper design and installation of the electrical system can result in serious injury or
death. Adhere to all applicable marine regulations (United States Coast Guard [USCG],
European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards they
reference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers
[SAE], International Standards Organization [ISO], etc.) for the market in which the boat
will be sold.
A battery switch may be desirable to allow the power to be turned off when the boat is not
in use and to allow switching between batteries in multiple battery applications. Certain
industry standard and regulations require the use of a battery switch and should be
consulted for requirements.
• The intermittent rating of the switch shall not be less than the maximum cranking current
of the largest engine cranking motor that it serves.
• The minimum continuous rating of the switch shall be the total of the ampacities of the
main overcurrent protection devices connected to the battery switch or the ampacity of
the feeder cable to the switch, whichever is less (ABYC Standard).
• Connect the battery switch into the positive (+) battery cable as close to battery as
possible.
• The switch should be located in a readily accessible location for use in an emergency.
• The switch should never be turned off while the engine is running to avoid damage to
the alternator. Switching between batteries should also be avoided while the engine is
running (unless the switch has been specially designed for this purpose).
• The switch should not be used to connect multiple engines to one battery (or battery
bank). See Multiple EFI Engine Battery Precautions.
Finding Other Diagrams
NOTICE
Refer to the appropriate Mercury MerCruiser Diagram Binder for wiring diagrams or other diagrams not found
in this manual.
Power Harness
IMPORTANT: On all models equipped with DTS or Emissions Control you must install the
appropriate power harness for your application. If your application is equipped with DTS
and Emissions Control only one power harness is necessary.
1. Connect the power harness to the battery. Ensure the lead with the fuse is installed
onto the positive battery terminal.
2. Install the lead without the fuse onto the negative battery terminal.
Page 8A-14
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Electrical System
3. Secure the battery cables and the power harness leads to the battery with hex nuts.
Tighten the hex nuts to the specified torque.
Description
Nm
lb‑in.
lb‑ft
Hex nut
13.5
120
–
4. Secure the power harness to the battery cable with a cable tie.
3711
Battery Isolator
! WARNING
Improper design and installation of the electrical system can result in serious injury or
death. Adhere to all applicable marine regulations (United States Coast Guard [USCG],
European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards they
reference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers
[SAE], International Standards Organization [ISO], etc.) for the market in which the boat
will be sold.
You can install a battery isolator to charge of an auxiliary battery used to operate the
accessories. The battery isolator will allow the alternator to charge both the cranking battery
and auxiliary battery simulataneously, while preventing accessories connected to the
auxiliary battery from discharging the cranking battery. The alternators used on Mercury
MerCruiser products are equipped with a special external sensing circuit to ensure optimum
charging performance in these types of applications by compensating for the voltage drop
across the isolator.
A special isolator is required for multiple engine installations where the cranking batteries
are to be charged from a common source. See Multiple EFI Engine Battery
Precautions.
IMPORTANT: Mercury MerCruiser cannot be responsible for problems resulting from
installation of the isolator. The installer and the isolator manufacturer must ensure that the
installation and any modifications to the Mercury MerCruiser product comply with all
applicable standards and regulations, including (but not limited to) wire size, type, routing,
terminals, and overcurrent protection.
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Electrical System
Battery Isolator Diagram
f
A
B1
a
ORN
RED/PPL
PPL
RED/PPL
PPL
B2
BLK
RED
ORN
BLK
ORN
ORN
a
RE
RED
D
b
b
d
BLK
BLK
c
BLK
BLK
d
e
24376
a - Alternator
b - Starter
c - Cranking battery
d - Ground stud
e - Auxiliary battery
f - Isolator
IMPORTANT: Cutting the orange wire flush with the wiring loom will result in damage to
the other wires in the loom.
The splice wire must be a minimum of 8 AWG.
1. Disconnect the orange wire from the alternator battery terminal. Splice the wire to the
orange wire and connect as shown.
2. Insulate and seal the end of the wire with liquid neoprene and heat shrink tubing.
Page 8A-16
90-863758070 APRIL 2008
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