Mercontrol Wiring to 1978 Mercury 500 Thunderbolt

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lgaytan

Petty Officer 2nd Class
Joined
Jul 15, 2015
Messages
109
Hello,
I have trouble starting up the motor I turn the key and have intermiten fails, sometimes it starts and sometimes it doesn't, some years ago I repaired some wires that were completely destroyed, rusted and falling in pieces, I saw yesterday while trying to crank some smoke comming from those connections so I believe cables are damaged again, any ways I will try to repair them but mostlikely I would like to replace all the wiring. Can anyone share a wiring diagram for this harness and if there is a Part Number to purchase? I want to try to repair first but maybe purchasing a new one can be an option as well.

Thanks
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,411
Replacement of the engine harness is usually a good idea at this age of th wiring. Wiring harnesses should be avail on the web. Try surplusunlimited.

Check the boat side of the wiring as well. Those harnesses are also avail, but more costly.
 
L

lgaytan

Petty Officer 2nd Class
Joined
Jul 15, 2015
Messages
109
So I went the easy route, my harness had like 2 foot extra in length so I was able to just repair the damaged wire and is working good now, I did noticed all the insulation of the cables is falling into pieces so I plan to change the whole harness soon.
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,411
Usually the engine wiring harnesses are too far gone to reinsulate them, as the conductor lasts longer that the insulation, but not forever.

Also, check the quick disconnect plug. Wires like to break inside them.
 
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