I'm replacing the factory AM radio in my 69 GTX with one of those repro AM/FM thumbwheel units. There are apparently 2 voltage leads going to the radio, same for old and new. One is for when the ign. switch is on to run the radio, the other one supplies power to light the dial only when the lights are on.

My dash lights have never worked, and checking at the fuseblock I get a very low steady flickering from 0-to-2 volts at the "INST" fuse. This is measured from the supply side with the fuse removed.

SO... where's my voltage? I tried to trace this orange feeder lead out via the service manual, but it just says "To Body Plug". Any ideas?