check the grounding side of the wiring to the bulb, do a voltage drop test on it, a bad ground causes loss of voltage which causes higher amp pull which then causes the contactors to burn up.
before that, read the wattage embossed on the headlamp housing itself to make sure you are not using higher wattage bulbs than required because that will cause this issue too. Headlamp bulbs and the housings are chosen as a pair, do not install higher wattage bulbs as that will overheat the headlamp itself and overheat the wiring too.