Bad switch?

[Got JOB]

Motor only cranks with key held in start position. Have replaced ECU, ballast resistor. Right now have a jumper from starter relay to ballast and car will crank but will not shut with key. Have to remove jumper to kill it.

[Bullitt-]

Could be the switch or any connection of the blue "run" wire or the ballast resistor. With the ignition in the "run" position check if your getting about 12V to the blue wire connected to the ballast, if not there's a issue with switch or wiring, if so the ballast is probably bad. You can test the ballast with an ohmmeter, should show about 1-ohm resistance.     

[Got JOB]

I suspect the switch but needed others opinions. The harness has never been cut and the car cranked fine this morning then when shut off would not crank back. I ran the jumper after changing the ballast and ECU didn't help and got the car back home. Thanks for the suggestions.

[Chryco Psycho]

Change the ballast first

[Got JOB]

I have changed the ballast with no result. My jumper wire runs from relay to the blue wire pin so I think the ballast still has to work cause the car will crank that way. Just will not cut off with key. Have to pull jumper to kill motor. Jumper has bypassed run circuit. Just seeing if I have missed something before I tear out old switch. Thanks

[Sinatra]

One last thing I'd do would be check your bulkhead connections and the ignition switch connector near the column.  A loose or corroded wire could be causing the problem.

[Got JOB]

Got lucky. Loose connector.