68 RR 383 finally got the engine in it cranks an starts but when you let off the key it dies anyone know what the problem may be ?Thanks to alll

Key switch or ballast resistor.....

Likely losing power to the ignition system.

Or its a wiring issue.

Usually the start circuit provides a full 12 volts to the ignition system during cranking, then after the key is let off, it runs throught he ballast resistor.

Turn the key to on without the engine running, likely there is no power to the coil.

Course, I dont know what your ignition system is like, oem aftermarket...ect..

99.9% of the time it will be the ballast. Classic symptom and good info in the 'tech' section.

It has a stock ingition system in it. Thanks

(1) pull the yellow "sol" wire off of the starter relay to disable the starter. (2) key "on" (3) jump starter at the starter relay (large batt stud to brown wire next to it) to crank it & see if it fires

Got it running. Had it 15 years & it finally starts & runs. Now its time to work on the body & interior. It was the ingition switch. Thanks for everyones help.