[68 Stepside]

Yeah, try the ground strap from the engine to the frame. And from the engine and frame to the body wouldn't be a bad idea either. I had a nasty electrical gremlin when I was driving my 68, if I didn't have the shifter (auto) in exactly the right spot, my headlights would go ape. If I shifted it manually, I'd lose power to the engine, and the headlights would occasionally turn all the way off. I put a large ground strap from the engine to the firewall, and that was that. No more gremlins.

Good luck.