car won't start until I release the key from the cranking position.

Bad Sport said

The one and only time a ballast failed on me, I could start the engine and as long as I held the key just right it would stay running.

As soon as I let go of the key to the run position, it would die.

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this is correct. Other posts here about dual ballast resistors are not.
If the ignition module has been replaced within the last 10 to 20 years, it likely has only 4 of the 5 contact pins. This means its more modern circuitry can operate on full system voltage and one half of a dual resistor is no long used or required.
Then again, if the dual ballast is present, I suppose those unused wires and connections could cause a similar condition.
Good luck