I installed a new hundred amp alternator on my 74 1.8 L 914 a while back. I was using the old wiring harness and ended up smoking the harness. Ended up blaming it on a short period I had the alternator checked out put in a new voltage regulator and installed new wire harness. Well today again it’s smoked the harness. The first comment everybody would make is that I had a short. I would’ve agreed with that possibility the first time but the second time I was more than meticulous to make sure I insulated everything to prevent that from happening.

So my question is, with a 100 amp alternator replacing the old 55 amp alternator is it too much amperage running through that gauge of wire and causing it to get too hot and melt? I’m thinking this might be the case since I’m going to have to replace it now for the third time. I’m getting the old Bosch alternator rebuilt and another new wiring harness. I would appreciate anybody’s thoughts or comments on this or if anybody else is run into this. Had the car running for about a half hour before it decided to do this today

Good question that I not really qualified to answer. Seems like what you're doing has been done before though. I can give you a

Which wire(s) is smoking? I have built a couple ALT harnesses with larger gauge red cables to the starter motor at the customers request because they said they had larger alternators.

Hopefully one of the EEs here can opine on what should be specified and where.

Hey Jeff yes of course it was the larger wire that goes from the starter to the alternator. Frustrating when this happens for the second time same alternator which is the higher amp alternator. I have yet to pull the harness out but if it is simply that one wire I will probably just run a single wire back to it much larger than this one. Otherwise I will be giving you a call to order a new harness. Thanks

In general I would say no, the 100A alternator did not melt the wire. With the 100A alternator, you're just providing more available current to the vehicle system. If the system doesn't need more current, you may never see 100A.

My guess is there is a short somewhere. I've heard with some new alternators that the stud which the heavy wire to the starter is connected sometimes contacts the rear cover and shorts out and melts the wire.

Do you have a picture of the melted wire?