I have a 340 in a 72 dart with electronic ignition. Recently i started having an issue with it starting. It cranks fine but won't start until i am letting off the key then fires. I put a new box and ballast resistor on it, still have the problem. Any ideas? Thanks

this is the 'classic' bad ballast symptom. i know you said you replaced the ballast but...

try jumping the ballast by connecting the wires together and see if it starts. you won't damage anything running it for a short period of time.

OE 5 pin ECU/4 terminal "dual" ballast or 4 pin ECU/2 terminal "single" ballast setup? pull the yellow with tracer wire from the starter relay to disable the starter and turn the key on and (1) the coil positive primary terminal and (2) the blue/yellow ECU terminal must be hot in ign1 "run" for the ign to function. If not, check the bulkhead & work forward or backward to find the open. grab your meter. EDIT only need to pull the yellow w tracer wire off of the "ign" terminal on the starter relay if you are checking things out in the ign key to "start" position. I'm just so used to checking both back to back

If changing the ballast didn't help, it's likely the bulkhead disconnect.

Maybe I am reading this wrong but does he not say it wont fire until he lets off the key ? To me that means no spark while cranking but it does fire with the key in the on posistion which would not be a ballast problem. Ron

Correct. Bulkhead connector. To the OP, disco the connector and clean the terminals. You will fix it.

Thanks guys, I'm still messing with it. I have a remote starter button hooked up under the hood and it starts fine. I been messing with the bulk heads and still when i turn the key to start with my test light hooked up the test light goes out.

FIXED !!!! It was the plug under the dash from the starter switch.

awesome and thanks for getting back to us!

Which plug (out of curiousity)