2000 E-Class sidelight problem

I had a short in the sidelight bulbholder (due to being supplied the wrong bulb, even though it was marked as for my car) and this appears
to have damaged the wire leading to the main lighting loom. There is an electronic 'diode' type thingy on the wire that my mechanic thinks is the problem. I approached the local MB dealer who tell me that the whole lighting loom needs replacing at a cost of 275! Anyone have other ideas?
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