I just went out did the jiggle test on all the wires I could lay my hands on. Nothing seemed loose and no amount of wiggling, pulling, pushing or otherwise resulted in an ignition cutout or discernible change in engine behavior.
I even went in the cab and monkeyed with the ignition key to see if it was loose or if any amount of wiggling would cut it off but that didn't result in a cutout either.
I don't like the looks of the wires to the coil anyway so I think I will replace them both. The positive one has one of those K Mart connectors where it ties into the main harness.
Those type of connectors were used by the prior owner to mess up the headlight wiring.
