There's a thermal cutout built into the headlamp switch. It tries to reset automatically because it's a safety issue. Sometimes the contacts get pitted and cause a little resistance. Resistance causes heat which leads to the cutout.
Adding plow lights adds to the problem if the truck's lights don't turn off when the plow lights are on. Aftermarket fog lights add a lot of current load to the switch. Factory fog lights are run by a relay.
When you pull the switch out, look for signs of a melted connector, burned terminals, or overheated rivets on the switch's terminals. Overheated terminals can be cut out of the connector and replaced. You don't have to replace the entire connector body. You will need to cut the wire(s) back far enough to find shiny copper. Splice on a new piece of wire and a new terminal and solder all connections. I prefer crimp-type quick connectors, but I solder them too after they're crimped. Be sure the terminals fit tightly when plugged in.
April, 25, 2009 AT 10:53 PM
Caradiodoc, I installed a new headlight switch and dimmer switch and still have the problem. I checked the wire from the hdlt swtch to the dimmer switch for short to ground w ohmmeter. I pulled the low and high beam wires out of dimmer sw connector and ran wire from hdlt sw through fluke amp meter straight to low beam wire and it worked and drew 7 amps. I did same with high beam and it drew 9 amps and went off after a while. I'm going to run new wires from dimmer sw to hdlts and see what happens. What I am seeing doesn't make sense.
I also found no burned terminals between hdlt sw out and dimmer sw in or out.
Thanx for your response,
April, 27, 2009 AT 5:34 AM
Happy to hear you know how to use an ammeter. What does it read when the lights go off? If zero, I'd start looking at the wire feeding 12 volts to the light switch, especially if it affects low and high beams. If only the high beams are affected, it could be the wire going to them. I was going to suggest an open common ground at the headlights but I'm pretty sure there is a separate one on each side. I know for a fact that's the case on the Dakotas. We had a '97 donated by Chrysler to my school. I installed a bunch of electrical bugs for my kids to troubleshoot, and one of them was a dim RF headlight due to an open ground.
I think I would start by attaching a test light to the feed wire in the switch, then watch what happens to it when the headlights go out.
April, 27, 2009 AT 10:58 AM
I did a lot of random checks on it but nothing was obvious. I think it is going to be a short that is being fed through the circuit breaker other than the headlights. I need a good wiring diagram of the entire vehicle. Can you suggest a good source for that. I need wiring diagrams of all the components also.
Thanks for your communications.
April, 27, 2009 AT 2:14 PM
The closest book I have is for a '98 Truck. It appears there IS a single common ground for both headlights. Both lamp grounds go through a " joint connector", but the joint connector has two different ground connections. If the problem is in this area, the wipers, front turn signals and running lights, and high note horn will not work at the same time as when the headlights quit.
Does this problem affect the low and high beams or just the high beams? If both, connect a voltmeter or test light to the 12 gauge Red / White wire on the headlight switch and monitor the voltage when the problem occurs. That's the 12 volt feed wire coming from the 40 amp fuse # 5 under the hood.
If only the high beam is affected, connect the voltmeter to the 16 gauge Light Green / Black wire between the two switches. Knowing what's happening on these wires will help determine were the circuit is opening up under load.
April, 28, 2009 AT 10:55 PM
I finally got it figured out. The new headlight switch I bought last friday was bad. I finally got fed up, unplugged the hdlt sw, ran 1 wire from hot wire to switch in and 1 wire from switch out to dimmer switch and still got 9.5 amps in and out of hdlt sw and they still went out. I eliminated any other possibility of short and realized the new switch was the problem. If I had access to a wiring diagram of the hdlt sw it would have been a lot easier. Can I have opinions of good service manuals. Back when I was turning wrenches I liked Motors first, Mitchell second, and chiltons was a waste of money. I would like to know what is good now.