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Universal M-12 Wiring

Aug 17, 2017
19
O'Day 272LE MYC
I'm reinstalling my Universal M-12 two-cylinder diesel in my O'Day 272LE and coming up with extra wires. (Yes, I know, I should have taken more/better pictures BEFORE disassembly.) It's going together okay except for two things: 1) There is a yellow wire with a red stripe and a crimp-on connector lug that the wiring diagram indicates should hook up to the starter solenoid. But there seems not to be anyplace to connect it. Am I missing some thing? If someone has a good picture, that would help. 2) There is a purple wire that the wiring diagram indicates should go to the alternator. It also has a connector lug crimped on. There is a yellow wire coming out of the alternator with a mating crimp on connector. The wiring diagram seems to indicate that connecting these two makes sense, but it would be comforting to know that someone else draws the same conclusion.
Can anyone help?
 
Aug 17, 2010
179
Oday 35 Barrington
ASSUMING that nobody has EVER modified the wiring, and that you have the stock alternator;
o - The Yellow/Red wire is the starter solenoid energize wire. This goes from the starter switch to the starter solenoid and causes the starter solenoid to energize.
o - The Purple wire is the voltage regulator field energize wire. It goes from the ignition switch to the voltage regulator. It is NOT needed if you upgrade to a self-exciting alternator.
Engine Wiring harness diagram.jpg
If ANYONE has touched the wiring, then all bets are off.

I recommend that everyone create and maintain a wiring diagram of their boat's electricall system as a living document. Below is an example of my boat's (O'day 35 with Universal M25 and a 90 AMP Leece-Neville alternator) wiring diagram as it was configured in 2015 (I don't keep JPGs of my current config).
Schematic 2016.jpg
 
Last edited:
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Aug 17, 2010
179
Oday 35 Barrington
Stu's post above reminds me to remind you - replace the trailer plug connectors in your harness with terminal strips if you have not done so already.
 
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Aug 17, 2017
19
O'Day 272LE MYC
Found the terminal in question. I had to unbolt the alternator to get to it.
Thanks!