Headlamp wiring

[slmecho]

I'd appreciate any help on the following dilemma: I traded an H2 for a 2007 SLK-280 w/ 59K miles from an import dealer. While having the low beam lamps replaced the tach said the plastic coating was nearly all melted from the wiring on the front end. He showed me pics of it &, indeed, he is correct. The tech wrapped the wiring with electrical tape for now, but I'm concerned as to why this could be happening. Coincidentally (?) the R foglamp & R marked lights are both blown now. Just wondering if anyone has had any issues with this too. Thanks