6066 (1960-1966) GMC Truck Club

I assume the battery is fully charge. The generator will not be able to put out enough current at engine idle to keep the engine running and will require the battery to fill the current demands. This also mean if the heater blower is running or your foot on the brake it will be on the battery until engine rpm comes up. For the engine to die you have a bad connection somewhere.

You will need the factory wiring diagram to help trace out this problem.

With a digital volt meter check the following:

Turn the headlight on, ignition switch off. (If repair are needed be sure to turn off the headlight and disconnect the battery negative cable before working on the wires. Then reconnect the cable turn the head lights back on for testing.) When using the volt meter it should indicate less than .25 Volt DC. The lower the better (ideally .1 Volt DC or less). Higher reading indicate a bad connection. If you find any connections that is blacken, insulation melted, or improperly connected it will need to be repaired first. All connections should be cleaned with Scotch Brite.

Attach the meter black probe to the frame for a ground. Measure the voltage on the battery negative post. If there a problem disconnect, clean everything, and assemble then retest. If good go to the next step.

Attached the red probe to the battery positive post (the following tests is performed with the red lead attached to the battery post). Check voltage drop on the starter large stud. Then check for power at the fuse block. Keep going until you see a voltage drop. Make any repairs as necessary and retest.

I had a similar problem where I had replace my positive battery cable with one from the auto part store. A couple years later the ring terminal the factory put on it was bad and causing intermittent starting and not charging the battery.

If more help is needed let me know.