Found out that the connector AND the socket on the tail light fixture has shorted due to the bad ground. This is a frequent BMW problem from my research. The ground brown wire is 1mm but the connector & socket pin & female for the ground is undersized, no wonder it gets hot & melts. BMW should have recalled this, but they haven't yet to my knowledge. So, I've ordered a new OEM tail light assembly on line ($165) & new connector w/bushing ground wire ($10). I'm going to splice the ground wire into the new harness/connector & reinstall the other wires & hope it wall works back to normal. Wish me luck, I'll keep y'all posted. Happy New Year!