[dmjlambert]

I don't think you need to look any places in the wiring and grounds for the melting connector problem. The problem is at the melting connector. Resistance there causes heat. When you replaced the connector before, did you only replace the plastic connector and insert the old terminals with old wires into the new plastic connector? If so, I think it is time to replace the connector with terminals/pigtail wires and use soldered connections and heat shrink tubing to connect to the wires of the cut off old terminals/connector. Add solder to the crimped terminal to wire connections and make sure you see the solder wicking into the wires and look for a shiny solder connections. Use 60/40 rosin core solder, that good known to the state of California as being extra dangerous stuff.

Other than right there at the hot connector, the other thing to check is voltage at the battery with engine running higher than idle. If higher than 14.5 volts you may have an overvoltage problem.