1986 OMC 5.0L coil hot and wiring hot *PROBLEM SOLVED*

[newfiez]

You have something shorting out and the ALT is trying to keep up. The 15.2V on bat 1 tells me the sense lead telling the ALT what the voltage is, well its not connected somewhere. The ALT is running wild and trying to get the voltage up because it either doesn't see the 15V or it sees it somewhere else which is dropping the voltage.

Not a OMC expert by any means but maybe the sense of the ALT is coming from the coil resistor wire instead of from the battery

The engine is wired exactly like the diagram on page one. You may be right, I have to disconnect the sense wire at the joint, and run it to the battery or starter wire. The weird thing is, when I switch to batt 2, the voltage output drops to normal on the alternator.

 

[newfiez]

Sounds like your sense line is wired to battery 2 only.

Disconnect the sense line and wire it up to the output of the alternator itself and try it. An easy test to do and many alternators are wired up that way now anyway.

Thanks bruceb58! The problem is solved!

I wired the sense wire directly to the alternator output, and here's the results:

Engine at idle,14.3-14.5v on batt 1, or both, or batt 2, coil + 8.6v.
Engine at 1700rpm, 14.5-14.8v on batt 1, or both, or batt 2, coil + 10v.

Coil is hot, but not boiling, resistor wire really warm, but not hot, and alternator warm not boiling.

Problem is now solved, thank you even for your input.

 

[Lou C]

Aha had the same problem a few years back. My batteries were not lasting long and I noticed that my charging voltage on the dash gauge varied a bit at certain rpm. Decided to get a new marine alt from ARCO. In the box the instructions said to check the charging voltage after installation because some OMC's will develop high charging system voltage. With the dash gauge reading 13.5V, I was getting 15.2 at either battery. They explained that due to the way the sense circuit is wired, you can get excessive resistance in those splices and the sense wiring is being affected by this resistance causing the alt to over charge the batts. Their recommendation was to do as Bruce advised above. So I removed the sense wire at the alt and taped it up in the harness. Then ran a jumper from the output terminal on the alt to the Sense terminal on the alt and problem solved. I guess if you wanted the most accurate measure of the battery state for your sense reading you could run the Sense wire back to the common stud on the battery selector switch. No problems after wiring it this way. My dash gauge reads low now but the gauges are original and I'm sure there is resistance in the old wiring.