[67-LS1]

Thanks for the input. I have two braided ground straps that go from the heads to the firewall. I have one other that goes to the frame. I also have a ground cable going from the front of the block to the frame where it meets another cable that goes to the neg battery terminal.
On the 12V+ side, I have a 12g wire running from the fuse block through the ignition switch and back through a connector on the back of the fuse block directly to the starter terminal. There is no additional relay(s) in the circuit.
The + side of circuit is pretty much stock 66 Chevelle with the new correct wire end for the starter soldered to the end. So that wire is 58 years old.
Is there a way to “load test” the circuit so I can see what might be drawing the voltage down to 6v?
I’m out of ideas.