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

nuttyprof said
Not if it is a dual ballast resistor, you could have a good run side but a bad start side. could be switch, wiring/bulkhead connectors, or ballast. Check for power in start at coil, bulkhead, and switch. That will allow you to isolate the problem, you might even see a lose/bad connection while getting to those places to test.

Thank you. :D 1973 car (probably dual ballast)

So always start with the easiest thing to fix and work your way along as necessary.
Start at the coil positive side and see if there is power when cranking.
No matter how messed up the wiring or what anyone before has ever done to it, that is still the first place to check.