i need a wiring diagram for the headlight switch on a 1992 dodge ram 1 ton cummins diesel 5.9L. i need to repair the connections in the harness after the terminals burnt and melted together, anyone got any insight as to what caused this problem. first i lost running lights, then all lights but hi beam, and then dash caught fire, yes the headlight switch burned
. the ignition switch has a burnt circuit and the harness to the multi switch shows signs of damage from heat in the circiut. the vehicle in question is a 92 dodge ram 3500 cummins diesel truck?

 

Full headlamp current goes through the switch. Connectors age, resistance in them goes up. Current through resistance = heat. Eventually it snowballs downhill.

If you added a bunch of chicken lights, that part of the switch is not thermally protected, and could burn down the whole shebang.

Permanent fix is putting the headlamps and maybe clearance lamps on relays.

Here's the 93 diagram, with wire colors. It should be the same.

 

Also check and make certain your windshield is not leaking. Mine was, and was dripping directly on the headlamp switch. the resulting corrosion created a LOT of heat, and cooked the switch.

 

Good advice above. I've seen a lot of burnt up headlight switch connectors on those trucks, particularly the park light circuit on the duallies. Duallies are much worse because of the extra current on that circuit drawn by the cab clearance lights, fender clearance lights, and the identification lights on the tailgate. Many people then compound the problem by wiring their trailer tail light circuit directly into the circuit, so those lights are also drawing current through the headlight switch.

A complete repair starts with a new switch and connector, and includes the installation of a relay to draw all the park light power away from the headlight switch. Installing extra relays for the high and low beam headlights is a benefit as well.

You mentioned burnt up wiring at the ignition switch too. The causes for this that I have seen are a combination of the connector terminals loosening up due to the harness flexing when the tilt steering is used, as well as a heater blower motor that is wearing and drawing too much current for the circuit.
Again, you will need a switch and connector, and possibly a blower motor if it draws more than 18 amps on high speed.