1970 Challenger will not start HELP???

I've been fighting with my dad's challenger for a month with no headway... Problem occurred coming home from a cruise, he said the car just lost power and backfired. Just like you reached down and turned the key off.

The car will not start. 1970 Challenger fitted with MP electronic ignition... I can turn the motor over by jumping the starter relay under the hood but will not turn over with the key. The main red wire to the ignition switch is hot when on the off position but loses voltage when on the run or start position.

Tried a new starter relay, new ignition switch, different MP orange box, jumped ballast resistor, even went as far as changing under dash wiring to another used one we had, no change in problem...

What else could this be? Fusable link? I didnt figure so because of voltage in the off posistion.

Have you checked the Neutral safety switch?

Being a 4 speed car, i made sure the neutral safety switch was wired back, also tried grounding the terminal of the starter relay to the body. no change.

since it ain't cranking, have a helper hold the key to start and You under the hood see if the blue/yellow wire/terminal at the ECU and the coil positive primary terminal both have near batt voltage. for the cranking the yellow wire/terminal at the starter relay must be hot with the key held to "start" & if not check the bulkhead first then work upstream (back to ign sw) or downstream (out to starter relay) & you've grounded the "grn" terminal on the starter relay. I had a severe backfire then coasted to a stop exactly like you when my FBO black coil died. this'll get us started. EDIT it started missing for 45 minutes or so before it went out with a bang & blew up the muffler with a cloud of blue smoke. the guy in the next lane almost wrecked & likely thought he was being shot at

Robert, thanks for the info... I'll have to check those things the next time I get a chance to look at it.... It's 45 min away from me in my dads garage