All you need is a service manual, the downloads.....
BUT YOU must know for certain "what harness" you have, not only what year and model, but "what options" it came with. WORSE some years there was a couple of MISPRINTS in the service manual concerning the bulkhead
Sound like fun?
http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617
http://www.mymopar.com/index.php?pid=31
Was this originally an "automatic" car?
You will have to do with the 69 Plymouth manual
Engine bay is original page no. 8-117, page 333 or so in your viewer
Inst. panel is original page 8-132, pages 348 and 349
Notice that the OUTSIDE two wires go to
B2-18BK goes to "C" of the bulkhead connector (BlacK)
B1-18V goes to "D" of the bulkhead connector (Violet)
The center connection is your neutral safety, S4-18BR (BrowN) goes over to one of the two "push on" terminals of the starter relay
On the INSIDE of the bulkhead connector, "D" has changed to white, C has changed to violet, and the inst. panel diagram STILL SHOWS A SHIFTER MOUNT backup switch for an automatic (bottom right, page 348) and the two wires are marked "manual transmission backup)
Let's move up to "70"
In the "Dart Challenger" manual, this actually used Mopar style page numbers.
Engine bay 8-89, Inst. panel 8-98 - 99
Here we show black from the switch going to D of the bulkhead, same as above
We show the violet going to C of the bulkhead same as above.
Now we go to the inst panel page 8-98
This time, we show both C and D is a white
C, B2-18W, goes down to page 8-99, in at lower left Follow it clear to the right of the page, it goes to pin 6 of your rear harness connector.
D B1-18W goes up to the RADIO connector, RED. What they are doing, is using the radio to pick up power there. That should be hot anytime the key is in "run