Hurst pro matic 2 wiring
You need a wiring diagram. If you have the correct starter relay, it has 4 terminals. The two push-on terminals are the relay coil. One connects to the "start" wire which comes from the IGN switch, out through the bulkhead, to the relay. The other terminal goes to a harness down the back of the engine, to the neutral safety switch. It should have 3 terminals, the center one is the NSS, and the two outer ones are the backup lights. So the second terminal of the relay hooks to the center terminal of the switch.
If you hook that up, there is no reason to use the shifter. Seein' as how the wiring is a mess, I guess it's up to you.
You can get useable wiring diagrams over at "MyMopar:"
http://www.mymopar.com/downloads/1971/71ValiantA.JPG
http://www.mymopar.com/downloads/1971/71ValiantB.JPG
from here:
http://mymopar.com/index.php