Alternator/regulator over-voltage

[mowerandy]

A while back I had a little engine room fire that resulted from diesel soot shorting the starter motor high tension connector to earth (had an exhaust system fail, and was venting it from the companionway to get back to my berth - bad idea).
Anyways, some wiring melted - primarily the ammeter feed, which was duly replaced. Everything else appeared to work OK so a full re-wire was put off for the moment.
Some while later again, I am banging my head against the wall trying to figure out why the fridge wont run consistently, when I finally realised that it dies whenever the engine was running. Voltmeter on the main battery lugs and it shows 17.5 volts with the engine running, and normal voltage when not.

I am putting this out there hoping someone may have had this under similar circumstances, or be able to tell me what to replace...

Motor is an old 12HP Yanmar, Alternator was replaced at the time as it was badly burned. There is a voltage regulator box in the engine bay which may have got quite warm, but I have had the lid off and it looks very clean inside, all relays free, and no sign of melted plastics or coatings within.

I daresay it will be tricky to source a new regulator, but is that where the problem lies I wonder. Plenty of wires attach to the regulator box externally, but I cant claim to have any understanding of where they go or what they do.

All I know is that I am glad that the fridge has voltage protection built-in, and that I haven't had occasion to switch on any other electronics while the engine has been running.

Any comments/advice gratefully received...

[SailsWithFists]

Sounds like a dead voltage regulator.