melted Alt-to-engine ground. Why?

[BornInAFord]

I fried the plastic on the alternator-to-engine-block ground while turning over a new engine. What would cause this heat? Is it a sign the alternator is toast?

It is a used stock multi-wire alternator from the old engine with new wiring on my 1966. It worked well before putting on the new engine. The engine is a 302 with Pertronix II dizzy and late model high torque mini-starter.
Thanks,
Daniel

 

[C0V3R]

Probably a loose connection causing arcing. Otherwise a bad ground connection from the engine to the battery resulting in the current going through the alternator ground. Check your main ground strap.

 

[BornInAFord]

Probably a loose connection causing arcing. Otherwise a bad ground connection from the engine to the battery resulting in the current going through the alternator ground. Check your main ground strap.

You got it! A poor ground at the engine block bolt sent all the current back up through the alternator housing. A 12 gauge wire was never designed to take that kind of current.
Thanks,
Daniel

 

[C0V3R]

Good to know it helped! How did the engine startup go?

 

[BornInAFord]

Good to know it helped! How did the engine startup go?

It hasn't started yet, and I'm waiting on another set of alternator wires to come from NPD. With the melted wire jacket it also melted other wire coverings and I was not wanting to just tape it and go. I've waited this long... might as well wait another day or two.
Daniel