[gtmud]

The smell of plastic was probably one of two things, neither being any good. Either your headlight switch was melting or worse your insulation on the wiring was melting. I had this same problem on my 00' XJ with only, at the time, 30K. Lost headlights altogether. Took it to the dealer to find that the main wire feeding the switch(Red) had somehow gotten hot and melted the insulation off, (the wiring harness was near my
steering column). They spliced in another wire a no problems. Recommend taking your dash out, not to bad of a job and start looking for signs of melted plastic(insulation). Did the fuse blow? Should have, Once you find the burnt wire, start tracing it from its scource to its termination point, looking for any locations were it was rubbing against metal causing a short, also with a meter check your switch for high resistance, this will cause the wiring to heat up. Also check ALL the grounds for your headlights. Good luck.