low &high beam lights doesnt work one side

dealer replaced connectors as part of a recall on headlight assembly in 2010 by splicing new connector.s. march this year lights on one side failed to work. took it to dealer who said had burnt wires and had to replace complete headlight assembly ,cost was 642 dollars. I told them they had replaced the connectors in2010 . did not think it was right for me to pay for assy since it obviously did not fix problem. dealer was to contact gmc . got 200 off repair. I believe gmc should pay total replacement cost and fix the problem.. burnt wires usually means either wire gauge is to small or connector is undersize or headlight assy not vented properly. it is interesting to note thst fuses didn not blow