I no longer have a ballast resistor or the factory ignition box.
I'd like to know for sure but don't want to hack in to my harness. It's all still fairly tidy.
One thing you can do is check if the terminals are all connected together by the wires. In other words do some continuity checks. Do you have multi-meter or test light?
Another thing that would be very helpful is to make a sketch like above of the wires you're checking. Then mark it up as you're working.
In addition to checking for continuity, visually look for similarities and differences with an unaltered '71 Plymouth A-body wiring.
Look at the diagram in the '71 Plymouth Service manual and note color, wire size and cavity the ignition in the bulkhead connector.
The ones you care most about are:
Ignition 1, this is powered when the key is in RUN and usually dark blue.
Ignition 2, this is powered only when the key is in START and often is brown.
Then look at the connections on the car, its usually obvious when people make alterations or even repairs because the connecting terminals don't look like the factory ones.
For example, on my '67.
Connector on left is original, on right is a replacement.
Original terminal (removed from connector)
Replacement (but this style terminal may have been factory for '71)
When you see wire terminals like shown below you know its been altered or repaired.
Colors and wire sizes sometimes are different too. Mark up your sketch to what ever you find. Use the meter to see which ones connect together. Hopefully that makes sense.
* '71 would have been early for a factory ignition box.
But what does it now use for ignition? If there's no box, then its either points or an amplifier on the distributor like can be done with Pertronix or HEI.
Points will have one wire off the distributor, the others will have at least two.
Power for the ignition in Start somehow has been tied to the power for ignition in Run. Originally this was done at the ballast resistor, so see if you can find where that wire was moved.
You can use this to begin. Add the rest of the info such as where those wires are on the bulkhead connectors. Then see if they are there on the car..
Based on what you've written, these are the wire connections in question.
