another starting question

Fix one problem get another.. I know i've read this on here before but here it goes. Car starts only when you hold the the key down when you release it to the run position it dies.. I have replace the ballast resister its a 74 challenger 318

That would normally indtcate a bad ballast resistor, but it could be the switch or bulkhead connection. Jump a wire from the battery positive to the ballast resistor, and if it stays running, start checking the wiring from the ballast to the ignition switch. I'm thinking the bulkhead connector connection, but it might be the switch, or even a broken or burnt wire?

I am also thinking check wiring,
I have seen wires get smashed getting caught in the valve covers or air cleaners.
Use a continuity tester for the wiring.

KISS: Keep it simple: first, The easiest thing to try is the ballast resister.

NNO WRONG U GOT THE ING WIRES CROSSED

Ok i've changed the ballast resister twice still the same problem when the keys all the way forward it ran just fine let off and it dies.My next step is the igition switch. I've traced the wires out of the switch. The blue wire is hot with the key in the run position the brown wire is hot when the key is forward when you let off it has no power.

Ignition switch is most likely good, I would take good look at bulkhead wiring first.

jumper wire the ballast resistor and if it stays running...gotta be the resistor or somthing taking it out...would then have to be somthing in the wiring before it...You've changed that resistor twice...this way will absolutely eliminate that portion. (if points ignition,don't let it run long,if electronic ignition with a silver/blue or ornage box,change that out)

I changed the horn relay or starter relay on the fender and it works fine. I think im going to change to a MSD box so i wont have to go through some of this again