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

Had this issue, and what I found.

Run puts 12v to the ballast and drops V to the coil to about 7-8 volts.
Start bypasses the ballast and puts full voltage to the coil to help starting when the voltage is being pulled down by the high current draw of the starter.
* the key is - “Run” drops out when key is turned to start.
And the ECU is fed from the run side. - voltage to the ECU is backfed thru the ballast and anything else on the run circuit can pull the voltage down during cranking. - “Run” has instrument gauges, voltage regulator, and some people wire their electric choke to it. Any extra current draw on the “Run” circuit - fuel pump, tach, stereo, whatever, Pulls the voltage sown and the ECU will not get sufficient voltage.
* jump the battery to the run side of the ballast.
Bet it fires right up.
But won’t turn off till you pull the jumper!

Ymmv