My 68 Charger 440 99% stock motor will just shut off like I turned the key off at random times. It will then restart within 5 minutes and then run for several trips/days. I checked all the harnesses, coil, ignition switch, and can find nothing wrong except for the coil was leaking so I installed a new one. The car then ran for a couple of days and then today, boom, it quit again. The problem is not heat related, has quit cold and hot.


Any ideas anyone?

I'd say start by checking the ballast resistor.
I'd also check the voltage on the output side of the resistor.

Dying ballast resistor maybe it's cracked?

I know you checked the harnesses but some people have had that same mystery problem because the main bulkhead at the firewall was either loose or not making good contact with the connections.

Hows the fuel look. You might have some water in the tank and when it hits the engine they will not run on water, also crud in the tank can do the same thing, cuttin off fuel to the engine.

Happened to me last year.
360 with the FBO setup (box/coil/resistor and distributor set-up)
It was the CPU box (that was the only thing I changed). I changed it with another one they sent and it didn't happen again (now I carry a couple extras, different brands). Mine happened a bit more frequently, usually quit once every other trip on the road.
Very scary thing when it happens depending on where you are, and would take anywhere from several seconds to a few minutes to get it to restart.

Thanks for all the suggestions!!!!!

I'll start further testing. Maybe it's getting closer to fully failing as today after this post it died 3 times on three real short trips. Always started back up after a couple of minutes. two of the times car was stopped, other time I was cruising at around 25.

Things that are flat broke are easier to fix, that's for sure!

I'm going to grab a electronic box on the way in to the shop tomorrow.

Sounds like a classic bad wire connection. Could take a while to find. Good luck