1992 OMC 5.8L ESA issue?

Hello, I did some searching but didn't see anything that helped.

A friend an I just purchased a 1992 Seaswirl with the 5.8L OMC Cobra Outdrive.

There were a few issues but we got them resolved and took the boat to the lake, it ran fine for the first two days but on the third, as we were pulling away, the engine just died. Nothing worked, no starter, no trim/tilt, no gauges… And the Tach was pegged at 6K plus…

Resetting the 50amp breakers got the trim/tilt back, replacing the ignition switch fuse got the engine to crank but it wouldn’t start. Pulled a plug and discovered no spark when cranking. After checking everything we could think of, we decide to unplug the ESA module, low and behold, we had spark and the engine ran but we had to shut it off to get out of gear (no shift interrupt).

We were able to use the boat for the rest of the trip but discovered a few more issues, if we just idled the engine and shut it off, it would restart just fine, if we ran it at high speed, we would have to reset the starboard 50amp breaker to get it to crank again. The Tach was still pegged at 6K and the only gauges that worked were the water temp and voltmeter which showed around 16 volts.

We ordered a new ESA, but I’m concerned that it is not the root problem, if anyone has any thoughts on what could cause this would be greatly appreciated.

So, on the advice received from a different forum, we tested the voltage at the battery and we got 15.3 (at high RPMs), turns out the voltmeter in the dash is just pegged at 16 volts whenever the key is on. This is true for the trim/tilt gauge as well...

Received this advice over there, posting it here in case someone has the same issue;

"On some OMCs, you can get high resistance in the sense circuit which will cause overcharging. Try this: disconnect the sense wire at the S terminal on the back of the alt and tape it up in the harness. Then run a 14 gauge jumper wire from the S terminal on the alt to the large alt output terminal (heavy orange wire). Then start it up and check the voltage at the batts. If it’s lower like 14.2v just leave it that way..."

My response was;

"...we pulled the alternator to try and get it tested but couldn't find a place that had the capability to test a marine alternator as all the true alternator/starter shops were closed on the weekend and the auto parts places we tried didn't have specs or a harness. We'll try to get it tested this week and if it tests good, we'll try the suggestion from LouC.

Does anybody have any idea why the gauges would be acting so weird? The tachometer is just pegged past "60" no matter what position the key is in, trim/tilt & voltmeter peg as soon as the key is turned to on, fuel gauge doesn't do anything. The only gauge that works is the water temp.

Could it be because the ESA Module is unplugged? I didn't think it did anything but stumble the engine for shifting. Are there some other electronics that could have gotten fried?"

If anyone here has any thoughts I'd love to hear them.