Scott Blackford

first post. first time owning an older cummins. 98 12v. 2500 sport, 188k miles.

Headlights work, Cluster gauge and parking lights work but when I pull the headlight switch all the way out, the headlights work, cluster gauge and parking lights are off. at some point in the pull, the cluster gauge lights flash on. I can toy with the position of the lights and get the cluster gauge lights on but not while the headlights are on.

I added headlight relays as many of the forum posts suggest. I replaced the dimmer switch on the steering column as other posts have suggested. I changed the headlight switch harness and I swapped out the headlight switch 6 times. I can't find any sign of burned wires or any indication of a problem. I have not checked the grounds but if a ground was poor I would think I'd get different behavior. The lights on the cluster gauge when I hit the right position are bright and don't flicker. To me, it still points to a headlight switch-related problem. But after the 6 replacement with the same results, I'm too close to the problem and need some insight from others.

Any thoughts?

torquefan

My first thought was headlight switch and/or connector as well, but I think you can safely rule that out. The next place I would look is the headlamp relay wiring which has some possible problem areas that are specific to Sport headlamps.

The big thing to be aware of is that Sport lamps use two different bulbs: 9007 in the outboard hole, and 9004 in the inboard hole. While the same connector will fit physically into either bulb, they are not interchangeable because the two bulbs require the connector to be wired differently; for example, one bulb uses the center pin for the ground, and the other bulb uses one of the side pins for the ground. Applying power to the wrong pin on a bulb can, of course, cause the power to backfeed through the circuit and cause strange conditions like you are experiencing. If your relay harness is plug-and-play, you can just go back to the factory configuration and see if the problem disappears. If it is wired permanently, you will have to find pictures of the proper connector pinouts for each of those bulbs, and go through your relay harness to see if there is an error.
Hope this helps.

Scott Blackford

Thanks Torquefan. I'll look through a service manual I got and double check my connections.

AlpineRAM

As dumb as it may seem- did you check the fuses?
And also, there is a place on the drivers side fender where the daytime running lights module can plug in- I had problems with corrosion in that place.