All of the lights work on my '73 except the front and side left marker lights. The flasher, and directional work properly, but no power in either socket for running lights. There is power at the fuse box at the other end (black and white wire) when switched. #5 fuse. Should I try a jump wire from the fuse block to the front to test? Could the original wire be broken somewhere along the way in the loom back to the fuse connection? Weird.

How did you test the power at the socket?

You need to determine if it's the 12V power or ground.

With your voltmeter, measure the center (12V) contact of the socket to chassis ground.

With power off, measure resistance from the ground (body) of the socket to chassis ground.

If the front running lights work, then the issue is wiring around the socket.

I only have a simple test light. Bruce tested it with a voltmeter. No juice only to the side marker and the front socket. Turn signal works, as does the emergency flasher. Same wire goes to front, then side marker is dead in front, but not at fuse….