Trying to get my '70 340 running in an E-Body and it will not start. Seems to want to fire when you let off the key, so I tried a new ballast resistor and still no go. Is it the ignition switch? Any other ideas?

When you are cranking the engine over you are getting 12 volts to the ignition, when the engine starts and you let off the key the ignition is going through the ballist resistor at 9 volts. When you let off the key and the motor trys to start that tells you the balliast resistor is good and the problem is no 12 volts while cranking. Go to the main wiring harness thats comes out of the steering colunm. The 12 volt wire is a brown 12 ga wire I dont remember the position. It is # 22 at the bulk head connector. Good Luck

I had the opposite problem once. The engine would only run as long as the key was on start with the starter spinning. When you let the key go back to run, the engine died. That was a bad ballast resistor.

Thanks, 'Medic, I'll follow that wire and see if there is a short.

I did order a new ignition switch.

I've had the same problem and it was the ignition switch.

Had a similar problem with our 70 318. The distributor pickup was bad.

Thanks for all the replies, everyone. I will try everything and start with the ignition switch as soon as it gets here.