Assuming you are fitting the correct wattage and type of bulb?...then electrical connectors melting usually means there is a poor connection nearby. A poor connection creates resistance, which creates heat. Heat increases resistance, and it becomes a vicious circle! If dirty then clean all relevant nearbycontacts back to bare metal, then put suitable electrical grease on them. Make sure there are no hidden cracks in cables (this is very possible) by cracks I mean INSIDE the insulation, the conductor can become cracked, causing resistance, heat etc. etc..