Odd electrical problem on mercruiser 350 ski boat

[Beb123]

I have a 2000 Ski Centurion v-drive with a 350 Mercruiser engine. Yesterday it conked out on the lake and I’m trying to figure out what happened. We were at idle getting ready to ski when wisps of smoke started to come from under the dashboard. I shut it down immediately and looked and felt under the dash to see if there were any obviously burnt wires or otherwise - couldn’t see anything. I waited a while then started it again and headed home. No smoke… but halfway home the engine overheated. I shut it down again and took a look - broken serpentine belt. Got a tow home and replaced the belt. Engine fired up no problem - engine temp was fine and I didn’t notice any smoke or smell after a few minutes of idle… but I noticed that the dash volt meter was only showing about 10 volts when it’s normally 14-ish. Alternator connections checked fine - nothing loose and belt installed properly. I tested the alternator by disconnecting the battery while engine was running - engine died immediately. I pulled the alternator (23 years old…) - nothing obviously wrong though the bearing is pretty rough. Not sure if there’s any way to bench test it at home. I took to a parts store and they said they can’t test marine alternators. I’ll get a new alternator as this one is certainly past it’s useful life even if it’s not dead.
So I’m scratching my head to figure out why all these things happened simultaneously and what could have caused the smoke. Seems too coincidental to be isolated issues. If the alternator crapped out, could it have both broken the belt (maybe due to extra friction) and caused some short that heated a wire in the dash? Would the broken belt have caused some kind of short (not sure how that would have happened)? Is there some other component that could be bad that caused the alternator to fail and a wire to burn? thx

 

[Bondo]

If the alternator crapped out, could it have both broken the belt (maybe due to extra friction) and caused some short that heated a wire in the dash?

Ayuh,..... Welcome Aboard,..... This, ^^^, is My waGuess,....

 

[dubs283]

Disconnecting the battery while the engine is running will surely damage the alternator. Time to replace

When was the serp belt last inspected/replaced?

Can't test a marine alternator is code for "we can't even test any alternator". Very few auto parts stores had a setup to bench test starting/charging accessories 30 years ago

Smoke from under the dash in my mind means either electrical/wiring cooking or the operator heater fan was running and you saw smoke from the cooling system without ample/any raw water supply through the heater core. A bit too toasty

 

[Beb123]

Disconnecting the battery while the engine is running will surely damage the alternator. Time to replace

When was the serp belt last inspected/replaced?

Can't test a marine alternator is code for "we can't even test any alternator". Very few auto parts stores had a setup to bench test starting/charging accessories 30 years ago

Smoke from under the dash in my mind means either electrical/wiring cooking or the operator heater fan was running and you saw smoke from the cooling system without ample/any raw water supply through the heater core. A bit too toasty

Thx - am getting a new alternator. Serp belt was at least a few years old (probably more). I believe the smoke was from electrical due to smell (and there isn’t a heater in the ski boat). What under dash wiring could be related to failed alternator/belt?

 

[Bondo]

Thx - am getting a new alternator. Serp belt was at least a few years old (probably more). I believe the smoke was from electrical due to smell (and there isn’t a heater in the ski boat). What under dash wiring could be related to failed alternator/belt?

Ayuh,.... A spike to the volt gauge,..??............

 

[kenny nunez]

Is the bilge open from the engine compartment to the front of the boat?

 

[dubs283]

A spike to the volt gauge,..?

In this case I'd get comfy on my back looking up behind the dash for shiny wire casings. The brittle kind w/burnt ends

 

[Beb123]

Is the bilge open from the engine compartment to the front of the boat?

Not really - it’s a v-drive and there is a big water tank in the bilge between the engine compartment and the dash. Would have to travel a long way and be a heck of a lot more smoke in the bilge for that to have been the origin. Smoke must have originated under the dash somewhere.

 

[Beb123]

In this case I'd get comfy on my back looking up behind the dash for shiny wire casings. The brittle kind w/burnt ends

Yep - nothing obvious but lots of wires disappear behind partitions. Will dig deeper.

 

[Beb123]

Closing this out (hopefully) - I took the alternator in to a local shop and it was trashed. Bearings and guts all bad. They rebuilt it for $100, less than the cost of a cheap Chinese one on Amazon. Will reinstall and hopefully it will do the trick.