no back up lights

Key must be in run and transmission in reverse. The two outside terminals on the switch. Should be easy to troubleshoot Your's is a '70?

Here are "alternative" wiring diagrams:

http://www.mymopar.com/downloads/1970/70ValiantDusterA.JPG

http://www.mymopar.com/downloads/1970/70ValiantDusterB.JPG

Look at diagram A at top right of page and find your neutral safety swtich

On this diagram, they show the wires are black and black with tr, they physically come up over the top of the transmission, there may be a second connector somewhere, and go into the bulkhead connector. On this diagram they are calling them "C" and "D" of the connector. From there they go into the interior, where one wire runs back with the tail /turn harness to the lamps, the other goes to the fuse box, I believe the radio fuse

Also, you can download various factory service manuals from here:

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

If you go down the page there's one for a 70 Dart/ Challenger

http://www.abodyjoe.com/pictures/Misc. car info/70 Dart Challenger Serv Man1.pdf