Thanks Hank, will check tonight after work & let you know. Any chance you have replaced your horn relay ? Mine looks nothing like the ones offered at NPD or my local parts store.

No I haven't changed mine. Disregard my previous post. I forgot this is a 72 and the wiring is different than previous years. Power for interior should come from a lead down at the starter, not off a pigtail from the positive battery cable. I don't recall exactly how it runs but hopefully you can follow it back to the bulkhead connector.

Followed power across the fire wall to a spot in front of the fuse box. No drop in power anywhere under the hood that I can find. When checking the fuse box and moving the shifter it drops to just over 10v when the lights are on. I will keep looking.

I would pull the bulkhead connectors and look for corrosion on those contacts. They plug directly into the back side of the fuse block through the firewall.