Starting problems

My 70 cuda starts up then shuts down soon as I release the key. I was told to check the ballast resister with the key on with a test light.. I do not have any power on each side .

Ignition switch or wiring in between
FYI, ck the bulkhead connectors 1st

Wiring problem like mentioned, between ignition switch and ballast res. Most likely NOT an ign switch issue.

Not to hijack the OP'S thread, but I have a similar problem with my
'72 Duster. When I try to start the car, especially when it's hot...
it is hard to start. When I go to turn it over, and then let go of the key quickly, and slightly pull the ignition cylinder back, it will finally start the car. Has new battery/starter/coil/Accel ditributor. Also has a Summit brand electric fuel pump. Any idea's??

Hijack all you want as we are here to solve as many problems/issues as possible. I gain knowledge here every day. I would turn the key to "run" & grab my meter & the coil positive primary terminal & the ECU power terminal (red if OE/blue yellow if MP pigtail harness) both need to be hot.

Ok, thanks Robert

This may be over simplified but the start/run circuit is something like this. Both Start and Run wires pass through bulkhead terminal #3, pins 22 & 23. The reason I mention the bulkhead terminal is that old Mopar bulkhead terminals seem to have a degree of not being reliable.

You found the problem. Test this by bypassing the Ballast Resistor with a small jumper wire, and start the car to verify its bad. Once confirmed, replace the bad Ballast Resistor.

Mopars of this era used Start 1 & Start 2 power wires to the ignition. The car runs on less than 12volts by passing it through the Ballast Resistor to extend the life of the coil = Start 1 ( key in the on position). It uses a full 12 volts to increase the ignition output during the cranking phase of starting the motor = Start 2 (key in the cranking position.)

The two ignition power sources, namely Start 1 & Start 2 are mutually exclusive. That means only one of them is on at a time due to the design of the ignition switch (the key switch).

The switch between the two power sources is very fast as the key is released from the cranking position to the run position. That split second switch is enough to cause EFI conversion set-ups to have problems with starting and running, but not enough to cause problems with regular points or electronic ignitions.