Back Up Lights Dont Work

Simple circuit. The backup lamps get power from the fuse box, through the bulkhead connector, and down to one pin of the transmission connector at the switch. Then the switched side wire comes back up, goes BACK into the firewall and ends up in the kick panel connector, and back to the rear with the tail and stop/ turn lights

So pull the connector off the transmission, turn the key to "run" and see if you have power. If you do, short the pins together and see if you have lights

If not, it's a matter of finding out where it's lost. Pull the left kick panel, get to the rear harness connector, and use a continuity checker to see if the backup lights wire has continuity (to ground through the bulbs)

If so, check continuity from the wire in the dash side of the connector down to the transmission

To test the power circuit to the transmission, you need a LOAD so that you force some current, to show up bad connections. So rig a junk lamp socket with a stop/ tail bulb, and wire both filaments together. Turn the key to run, and one of the connections at the transmission should have power

Don't forget that aside from grounds, the socket connections themselves, as well as connectors are the no1 suspects

So you have the sockets, the kick panel connector, the bulkhead connector (twice) the connector you mentioned at the rear of the engine, and the connector at the switch.

The diagrams at MyMopar:

http://www.mymopar.com/downloads/1973/73ValiantA.jpg

http://www.mymopar.com/downloads/1973/73ValiantB.jpg

It shows the rear harness backup wire as VIOLET but CHANGES to WHITE at the kick panel connector, goes OUT the bulkhead connector at Z, AND CHANGES to BLACK in the engine bay, where it goes to one side of the switch on the transmission.

From the switch it goes (BLACK) back to the bulkhead at W. This is the POWER supply side of the switch. From the bulkhead it then goes to the fusebox.

I would bet that if you download the '72 shop manual it is essentially the same:

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download