I don't know that a ballast resistor can work for a bit, then quit. Then after cooling off work again. But I guess anything is possible.
The ballast resistor has a wire that goes from it to the positive side of the coil. The other wire from the ballast resistor goes to the ignition switch. There may also be another wire from the small terminal on the starter that either hooks up at the + side of the coil, or at the ballast resistor on the same terminal as the wire from the ballast resistor to the + side of the coil. (Don't remember the color off hand.
When the truck quits, take a volt meter or test light and see if you have power at the + side of the coil. You should, won't be 12 volts because it's going through the ballast resistor. If no power, go to the ballast resistor and see if you have power on either terminal. If you have power on the side that feeds the +side of the coil, then the wire between the coil and the resistor may be broken inside the insulation.
If you don't have power to either terminal on the ballast resistor then the problem is in the supply from the ignition switch, or even further back. I think the ignition switch is supplied power directly off of the amp meter.
