Should I re-wire my engine harness?

ttownthomas

Petty Officer 1st Class
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Jun 7, 2019
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The wiring on my boat is mostly original. (Twin Mercruiser 165 L6's). The wire on the motor side of the cannon harness has been obviously fiddled with as it is not nearly as tidy as a factory install. Due to a running issue I am getting ready to replace the resistor wire back to the cannon harness (which is also damaged). This means I will have to remove the tape and unravel about half the harness. The OCD in me says trash the engine harness and re-wire it.

My instinct is to cut the cannon harness off and add marine grade ring terminals to the boat side of the harness and run them to a terminal block affixed high on the transom and then re-build the motor harness from there.

Eventually I may do the boat side of the harness but it appears to be in pretty good shape

Is this a bad approach?
 

Chris1956

Supreme Mariner
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Mar 25, 2004
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28,398
The original cannon plug was/is standard for many years. The boat side of the harness may have been a Mercruiser harness that was modified or perhaps even supplied by the boat manufacturer.

Why not price replacement harnesses from MerCruiser, or aftermarket. I would think more than just the resistor wire is corroded at this point.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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the factory 49 year old harness is most likely NLA

however the wiring on the inliners is simple



getting wires in todays standardized wiring scheme to re-wire the engines is about $100 for the two engines along with some harness connectors. you would need to have the proper crimp tool.

standardized colors are here:

https://forums.iboats.com/forum/boa...03677-generic-boat-wiring-information-updated

you would need 25 feet of each of the following to re-wire your two motors:
16 ga black - ground
16 ga red - power
16 ga purple - ignition
16 ga tan - engine temp
16 ga light blue - oil pressure
16 ga yellow with red stripe - starter

and about 10 feet of the following:
6 gauge red or orange - alternator
6 gauge black - alternator ground

https://www.ebay.com/itm/16-AWG-Gau...hash=item3fc4ec5077:m:m8l5Vnr2Pv8fB4Hvzm8yijA

Then pick a round Deutsch connector for about $30 a mated pair

or you can find semi-custom harnesses with the cannon plug for about $150 each

https://www.michiganmotorz.com/cust...lQ0lPQ0ZS5GhUg_GWckfuhUa2rnfp0LRoCWbQQAvD_BwE

however wiring a motor is easy.
 

ttownthomas

Petty Officer 1st Class
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Jun 7, 2019
Messages
204
Is it better to re-wire with the standard colors? Will those aftermarket/mercruiser replacement harnesses mate up to my boat side harness?
 
Last edited:

alldodge

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Is it better to re-wire with the standard colors?

Not sure I would say a lot better because there were some design issues which were later fixed with changes. Things like adding a slave relayno amp meter and using standard colors are all good. If the original wiring works, then there could also say why change.

Will those mercruiser replacement harnesses mate up to my boat side harness?

The connector will attach but there are some pin out changes. As example

Old pin 4 Red/White come from Gen battery voltage
New pin 4 Purple Tan/Blue for Alarm horn
Old pin 10 Purple oil pressure switch
New pin 10 Brown/White trim gauge

My ease comment above should have also said that its ease to use a new harness but if helm is not rewired to code, then need to route wires not by color but what they are used for
 

alldodge

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And whats wrong with the ammeter?

And you need a larger wire going to/from the meter to read/transfer the amount of current
 
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