Motor is in a '57 Chevy pickup. Recently, a few minutes after firing up, my V8 morphed into an inline 4. Discovered only 1.5 volts was getting to passenger side coils & injectors. Could not detect any defect in power wiring between coils/injectors and underhood fuse INJB. Did though find a (14 gauge) ground wire with badly melted insulation in the wiring bundle inside engine compartment. Things got funky then. That wire was not near a heat source. A few inches from the PCM, the four small diameter PCM ground wires (pins 1 & 40 on both Connectors C1 & C2) were soldered to one end of the wire in question. The other end of that wire was grounded to rear of driver side cylinder head. Along the way, four other small black wires were also soldered to that wire. The melted section was between the soldered joints. After replacing the wire that had melted insulation, I got 12V to coils/injectors on both banks. Engine fired right up and performed flawlessly during 20 mile test drive. Here are my questions:

1. What could have caused the insulation on a 14GA wire to melt when there was not any apparent damage to the much smaller gauge wires connected to it?

2. The melted wire (with bare copper exposed in places) was adjacent to power wire to passenger side coils/injectors. Is it possible the exposed bare copper ground wire robbed most of the voltage in the undamaged, much smaller power wire?

Even though engine now running fine, I am leery the root cause of the problem has not yet been resolved. Do not want to get stranded by the side of the road.