back-up lights on 64 dart gt

There are somewhat usable diagrams here:

http://www.mymopar.com/index.php?pid=31

64 Dart:

http://www.mymopar.com/downloads/1964/64DartA.jpg

http://www.mymopar.com/downloads/1964/64DartB.jpg

The dotted lines and notations are the differences between automatic and stick. Automatics would have the reverse switch on the shift linkage inside the car, but stick cars must feed through the bulkhead and down to the switch on the transmission.

So first order of business is to find the backup light switch and see if it gets power with key/ on.

An easy place to divide the problem with the harness is the connector in the left kick panel.

That's illustrated near the top left of diagram "A"

Follow the wire from that connector, terminal "4" down, through the backup switch and (white) and you'll see that power comes from a tap off the wiper switch. "The thing" off to the top right of the switch is representing a switch mounted breaker.