Boating Industry of America Wire Color Code

Here are the standard wire colors used in the boating industry since the late 70s.   When trouble shooting an existing unit or re-powering a boat with a newer motor this is a handy reference.   Most boats with outboard motors use these standards but always double check in case some aftermarket changes have been made !

Black———————————All Grounds
Black with Yellow stripe———Magneto/short to Kill
Gray———————————-Tachometer signal
Yellow with Black stripe———Choke
Red———————————–Unprotected (12V+) from battery  (not fused)
Red with Purple stripe———–Protected (+12V) from battery    (fused)
Purple——————————–(+12V) from ignition switch
Tan———————————–Overheat sensor to warning horn
Pink———————————- Sending unit to fuel gauge
Yellow with Red stripe———- Ignition switch to starter solenoid
Yellow——————————–Charging stator to rectifier
Lt. Blue with White stripe—— Trim up
Green with White stripe———Trim down

Some more standard wire colors used on many inboard boats, always double check though, as some vary or may have been changed along the way!

Some standard colors for boats since 1980 are as follows:

** Motor
· heavy Red 10 gauge (main battery)
· heavy Black (main ground)
· Purple (ignition)
· Yellow (starter solenoid)
· Grey (tachometer)
· Brown (temperature)
· Blue (oil pressure)
· Brown with stripe (alarm)

** Accessories
· Pink (fuel sending unit)
· Yellow (blower)
· Brown (bilge pump)
· Grey (navigation lights)
· heavy Green (bonding wire)
· Red (miscl electrical add-ons , vhf , depth finder, stereo, radar, power supplies)


Most larger outboards have an in-line fuse on motor usually inside a small rubber or plastic fuse holder.
It is generally an extremely short fuse holder with a short 20 amp fuse in it.
It’s often located near the start solenoid on one of the red wires.
If that fuse is blown you will get nothing at the switch!
Can’t find it… you might check your owner’s manual for the location.


Here is a simple method of adding a 2nd battery that I use on my boat.  This is easy to set up from most existing wiring by adding a disconnect/selector switch & the 2nd battery.  

For me I normally only use the main motor as a “Get There” motor and then the trolling motor the rest of the day.  I keep all my electronics on while fishing and in the past (using a different trolling motor with less charging capacity) when only having one battery I have had it low enough that when starting the main motor the sonar would drop out because of low voltage.  This system pretty well isolates the main motor & yet when in the ALL position serves as my now normal run position of my trolling  motor Yamaha T8 which maintains charge on both batteries.

The reason for not wanting to run both motors simultaneously is that since both are actually connected if in the ALL position, without a diode to stop any voltage feedback where there could be possible damage to the newer main motor’s computer.

If I was just running around and not trolling with the small motor, then I would set the selector to #1 to power the dash panel and electronics, while the main motor would be on it’s own and operate fine because it is wired direct.


Trailer Light Wire colors

Yellow- left turn signal
Green- right turn signal
Brown – Tail lights
White- Ground

When brakes are applied power is sent to both the yellow and green.

You may need a taillight converter if you have a non US made truck or car.  This converts a 5 wire vehicle wiring to 4 wire to a trailer.


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