I had a similar issue with my '85 Mustang. The solution was to put a relay in the circuit. The switch would heat up and the lights would go out. The first time it happened, I was on a 3 mile long 2 lane bridge in the middle of nowhere around midnight. That was fun. Anyway, power out from the headlight switch powers the relay. Take power from the battery to power the outbound side of the relay, and the other terminal goes to the headlamps. Make sure the relay is rated high enough to handle the load. I don't recall the size I used, but I would go at least 5 amps over the rating of the fuse on that circuit. Good luck!