If you still remember what engine did this truck have? 6g72 mits by chance? and where was the resistor located?
Edward, You are a genius. We checked the ground on the coil first, it was OK. Then we located the resistor and checked with ohmmeter. It had continuity, but we went ahead and made a temporary jumper and bypassed it. Voila, started and ran perfectly. We I called my parts dist. however, I found you can't buy the resistor without buying the coil. He recommended I go to NAPA and pick up an automotive resistor. We did and the unit is working fine. Thanks a million.
my moneys on the resistor lol
i think there was another thread like this a few weeks ago
this unit may well have an external resistor coil, and the resistor has gone bad.(sometimes these burn up when the key is left in the on position and the unit not running) the resistor is bypassed in the start position of the key switch.
I have also seen this with the ground (negative side of circuit) of the coil case not supplying the negative side of the circuit. this can be if the coil is not tight in it's clamp, and/or the clamp itself not getting good ground, including from the strap from the frame to the motor. (too much paint of the frame can cause this) I would check and clean all the ground side leads, if for no other reason than all the other electrical related failures you have had.
there are also some of these units that over the years have had a break internal to the 12volt battery positive from key to coil wire (right near the coil) where the insulation is still OK but the metal of the wire has broken due to "sympathetic vibrations" because the motor and frame do not shake at the same speed, and the wire is what runs from the engine to the frame, try pulling the wire to the coil, if it stretches, then you have a break internal to the wire where it stretches.
sounds like a faulty key switch, you said that you tested the current in the run position, but I think that what you mean is that you tested the voltage or continuity. the circiut is not able to conduct properly under the load of actual operation probably due to a poor contact inside the switch.