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Tue Sep 04, 2018 6:39 pm

A few years back I did an alternator conversion to my 73 Thing. Worked fine until a month ago when it stopped charging. Brought it in and mechanic diagnosed it with a failed alternator. Replaced the alternator with a Bosch. I drive it 5 mins home and sits for 2 weeks. I start it up and drive it for .25 miles, generator warning light goes on and smoke starts coming out from behind the dash. Drive home... more smoke. I checked and the melted wire is the blue and black striped wire which looks to be the generator (now alternator) idiot light, which also goes to the brake warning light. Wire is totally melted and exposed for a good foot behind the dash. What could possibly be the issue? Thanks!

Thu Sep 06, 2018 5:04 am

More followup/questions to this issue. The melted wire behind the dash is a blue wire with a black stripe. it splits behind the dash and one end goes to the Generator/idiot light and the other to the brake warning light (which is always on, but that's another issue). From the wiring diagram posted here, I assumed the other end went to the alternator, but when I unplugged that wire from the alternator, the Generator/idiot light went out but the melted wire still has power. Help!

Thu Sep 06, 2018 8:08 am

Yep. The wire that goes to the generator is hot whenever the key is switched on. It get's power from the unfused side of fuse 1. It gets its ground from the voltage regulator (in this case the internal regulator in your alternator).

So when you turn the key to on, but haven't started the motor, power flows from fuse 1 to the gen light and then to ground through the voltage regulator. This is for the purpose of a bulb check. When the engine is running, the voltage regulator deprives the blue wire of its ground.

If I were you I'd be looking for someplace around the burnt wire where there might have been a dead short. But I've got to admit that the voltage regulator has always been a mystery to me.

Thu Sep 06, 2018 8:53 am

Captain Spalding wrote: Yep. The wire that goes to the generator is hot whenever the key is switched on. It get's power from the unfused side of fuse 1. It gets its ground from the voltage regulator (in this case the internal regulator in your alternator).

So when you turn the key to on, but haven't started the motor, power flows from fuse 1 to the gen light and then to ground through the voltage regulator. This is for the purpose of a bulb check. When the engine is running, the voltage regulator deprives the blue wire of its ground.

If I were you I'd be looking for someplace around the burnt wire where there might have been a dead short. But I've got to admit that the voltage regulator has always been a mystery to me.

Thanks Cap. I was wondering whether the short could be at the brake warning light. That blue wire is connected to the warning light and the warning light has always been loose. I suppose if that contacted the metal part of the dash, it could cause the short and wire melting. I'll check on that.

Wed Sep 12, 2018 7:48 am

Update: The only possible short I could find is that possibly the brake warning light could have been grounding on the metal dash. Otherwise, I couldn't find anything. I ordered a used wire from Mike at thingparts.com and it should arrive soon. Any suggestions/recommendations/tips on rewiring and soldering the new wire in behind the dash? Looks like the wire is melted until it goes into the big wire loom. So it has to be replaced from there to the generator idiot light to the brake warning light.

Tue Sep 18, 2018 4:17 pm

dagimp wrote: Update: The only possible short I could find is that possibly the brake warning light could have been grounding on the metal dash. Otherwise, I couldn't find anything. I ordered a used wire from Mike at thingparts.com and it should arrive soon. Any suggestions/recommendations/tips on rewiring and soldering the new wire in behind the dash? Looks like the wire is melted until it goes into the big wire loom. So it has to be replaced from there to the generator idiot light to the brake warning light.
Seeing as you're not sure the cause has been identified and solved, before you permanently install the new (used) wire, you might consider making a temporary connection with some generic hook-up wire and an inline fuse holder with an 8 amp fuse. Just twist and tape the connections and then test.