adamsbomb,
If there is a visible, white ceramic ballast resistor mounted somewhere, a check with a voltmeter on the side nearest the coil should indicate something on the order of 9 volts with the key turned ON. Cars of this era show a resistor wire as opposed to a ballast resistor, but regardless, the coil needs to see voltage when the key is turned to ON...the truck doesn't have to be running, but the key would be ON.
Good luck and keep us posted on this problem.
Stuart
