I recently repaired the pigtail going to a combo switch on the transmission of a 1978 Econoline camper van. The 4 wires were intermittently touching because the insulation had crumbled and disappeared near the connector. I have never seen plastic insulation deteriorate like that. The underbody is wide open. Could it be heat, or ozone, or what?
By the way, the resulting symptoms were horrendous. When 2 of the wires would touch the starter relay would get continuous power from the neutral safety switch line. It would touch the reversing lamp switch. Two starter relays and two starters burned up until I tracked this intermittent problem.