Electrical here we go again

[transam]

My 70 340 has been running fine. I went out to the heated garage a few weeks ago. Pumped and started the engine. Once the fuel got there she started right up. I put her in reverse and backed her out onto the driveway. I was trying to test the dash lightbar which has not seemed to be working.I pulled the lightbar down and I also undid the control switch panel on the left to maybe check wiring. I ran out of daylight. I got in, turned the key to start and put her in the garage for the night. I got a big backfire pop and then the car just turned over with no starting. It cranks real good and appears to want to start but as soon as I release the key thinking it will start, it just stops trying?? I do not think anything in the dash I am playing with has anything to do with the ignition. So, I went out there today, got in and turned the key. The car turned real nice and started right up? I ran it for a few minutes and shut it down. Waited a few minutes and decided to fire here up again. YUP. Same old ****. Yuens nice but will not stay running..... What should I be looking to go about checking. I do have an electronic mopar distributor with the orange box. This has been fine for years, so I know they are all installed correctly. This is driving me crazy. I do not feel like just being a guess what parts to change and would rather diagnose this so I learn some electrical. I do own a power probe for testing. What is the correct avenue to test this>

 

[Xcudame]

A lot more knowledgeable folks about electrical gremlins than me will chime in (thank God and the folks providing this site), but I start this off. Cold it starts and runs fine, then shuts off and won't start but turns over, correct? Once it dies after first starting it, with the key on, check for voltage at the ballast resistor. Check voltage at the coil. Check for a spark at the spark plugs. Sounds like it's getting fuel and electricity to the starter OK, so that kinda says the ignition switch is OK. Something is heating up from current going through it and causing short (usually an open, but we say short)!

What year is your distributor and orange box? I ask, because once our politician "betters" moved most of our manufacturing to Asia in the early 2000s, most electrical components are seriously suspect these days new out of the box!

 

[Challenger RTA]

I have to say

Xcudame is probably spot on!​

Hot wire it. Then you will know if it's the car's wiring.
To bypass all the wiring for the ignition hot wire it. Run power from the battery to the blue resistor wire on the ign 1 side not on the ICM side.
If you can start the car with ing sw but it will keep running until you turn the key off and remove the jumper wire. BOTH! If it stays running and runs good, it's the wire or connectors. Low voltage through a bad connection or connections.

If it won't start. It's an ignition component or ground.