Do you have a Bosch or Chrysler ignition system? If the cap is white it is a Chrysler sytem and your problem could be related to the ignition module with a poor ground connection. The ground wire is black and is either the second or third down. Take the connector loose and see ithe C-connector has opened up to where you don't get a good connection (this is a common problem). If the car has a tach you will see very erratic movement particular if the engine dies. Had this happen several times on my 82 245.

I beleive there is a Hall sender on my 82 and you don't have to take the distributor out to change the sensor.

I hope your are right on the wire from the ignition to terminal 15 as being the root of your problem.