A while ago, my alternator wasn't putting out, however the tach still worked, so I tightened the belt, cleaned all the electrical ends, that didn't work so I took the alt in, it tested bad, bought a new one from Blue Circle, it wouldn't put out either, started following the wires, that's where I found the problem.
I erroneously assumed, (should have read the archives better) that if I had a voltmeter, the harness upgrade had been done. It wasn't. In fact the plug behind the instrument panel was horribly melted and corroded, (luckily no fire) resulting in no continuity in the Alternator wire.
The gist of this post is not the Alternator problem, but to remind other owners, that no matter how many neat upgrades are done, how much electrical has been added, or how nice everything is, PLEASE SEE IF THE HARNESS HAS BEEN UPGRADED.
Stu and Ron and others have been warning us of this problem many times, but due to the fact I had a voltmeter, I didn't pay attention as close as I should have, I now know that in 88 we had voltmeters but still had the old harness. (in fact if someone were to ask me it the upgrade had been done, I would have said yes)
I am going to cut that plug out of there and either use a terminal strip, or hard wire the ends to the instrument panel. Then check the engine end. according to the archives, I should be able to run the output wire from the Alternator to the batteries instead of up to the switch as before. "right"?
The PO was a member of this site, many upgrades had been done, dedicated starter battery, combiner, propane locker, 4 T105's, glow plug solenoid upgrade, ect, and was very particular in what he did on the boat, all these neat things except the most important, the harness upgrade. So please check it out as I should have. (It is so easy to take a peek)
As Stu and Ron say, this is one upgrade that can save your life