Starting issue 70 Plymouth Fury

When I go to start the car with the key spins over will not fire if I leave the key in the on position jump the starter relay it fires right up. what's going on?

Ballast resistor. You are running a 4-wire unit? Possible ecu if converted to electronic ign, but not as likely.

I thought it was a ballast resistor too, I changed it twice and still have the same issue I did convert to electronic ignition and it has a two wire resistor.

(1) pull the yellow "ign" wire off of the starter relay to disable the starter & have a helper hold the key to "start" & you under the hood see if you have fire at the brown wire on the downstream end of the ballast & if not then find/fix that open (bulkhead is a frequent culprit). (2) How many pins does the ECU have & if its (5) then ohm the 5th pin (at the red/green pentastar pigail) to the ECU case & see if you have infinity or a reading. you said 2 terminal (single) ballast correct? An OE type 5 pin ECU with a functioning (has resistance) 5th pin REQUIRES a 4 terminal (dual) ballast & if an OE type 5th pin ECU has infinity on the 5th pin then it is shot. A parts house 5 pinner will by design have a dummy 5th pin (infinity) & is functioning & will work on a single or dual ballast as will a MP or replacement 4 pin ECU. holler back. EDIT always a good idea to pull a batt cable before switching the meter to ohms

Fixed it. Found the brown wire had come loose under the column at the ignition switch I plugged it back in and it works fine. Thank for the help everyone.