64 Plymouth Valiant Dies

You have original wiring? What for ignition system, IE points, Mopar ECU conversion, etc?

No1 suspect on these old cars is the bulkhead connector

Inspect/ replace the ballast resistor, push/ pull the connectors on/ off to scrub them clean

Pull apart and clean/ inspect the bulkhead connector.

Do the same with ignition switch connector. If you have strong nimble hands (Mine are arthritic) on some cars you can reach up and push/ pull the ignition switch connector to scrub it.

If the above does not give you results, go to Radio Sh##, etc, and get a 12V LED. "Rig" it in a simple manner with extra wire, etc, so you can hook it to the coil side of the ballast (if you have points or ECU) or to the supply voltage for MSD, other.

Run this out the rear crack in the hood, or a convienient spot in the firewall to someplace where you can see it. Next time it quits, you'll know for sure it's actually electrical.