Low voltage at gauge, no charge?

Darn, man. If the headlights don't work this sounds like probably the welded splice has broken. You will have to pull the cluster to check. the welded splice is a few inches away from the ammeter black wire termination, wrapped up in the dash harness. Once you get the cluster out, you can unwrap the harness working back from the ammeter. Follow that big black back

First one of these I ever found was in the early 70's in a friend's 68 RR. We had the cluster and part of the wiring torn out of the dash in his apartment parking lot. He was beginning to think I was an idiot AND I WAS TOO!!!! LOL