Dim lights suggest poor connections due to corrosion . So check ALL connectors and the earth plus all internal to the headlamp connectors..
You csnnot blame the mechanic for an electrical fault with your car.. I suggest there may be a short across the connectors leading to the smoke and melting... so any repair will have to include a 100% check of the headlamp internal electrics..
I suspect by the time you have repaired it and got it working properly, you may wish you had bought a replacemnet headlamp as getting beam alignment could be very difficult...after a repair as you describe.
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