I have a 1993 d350 and the when I turn on the headlights the running lights won't turn on with them nor will they turn on when I pull the switch to the first notch witch should be the only the running lights. I can tweet the **** a little and get the running lights to work but if I hit a bump or barley touch the **** they will go off. It seems like it would be in the switch that seems like the only logical explanation but I've bought 3 different switches 3 different brands from 3 different stores. PLEASE HELP

 

Have you checked the plug on the headlight switch? Those connectors can get loose and make intermittent connection. Also check the fusible links on the left fender and the fuse panel. I took my switch out of the circuit completely and replaced it with 2 toggle switches. I also have relays for the high-power headlights I have to take the load off the hi/lo switch in the steering column.

 

How do you wire them up to switches I was thinking about running them to a switch panel. Fuses are all good and pigtail is pretty new no loose connections

 

You just trace which wire goes where and wire them up. I ran the hot wire to both switches then one switch goes to the headlights and the other goes to the tail/marker lights. I kept the rheostat in the original switch to control the dash lights.

 

I'm with Mr. Smith. All of these first gens are hard on the head light switch in the headlight circuit. The 1 tons are also hard on them because of the extra clearance and marker lamps on the tail light contacts.

Seems weird that you'd have the same symptoms with different new switches, unless they all came from the same bad batch.

If you can approach the problem with a meter or test light and a diagram when the tail lights are failing, you should be able to pinpoint the failure.

 

 

They really should be on relays.

 

The exactly the same thing is happening to me. No running lights with headlights.BTW my headlights are on relays.
I change the headlight switch and it didn't help. Check grounds,connections
and fuses, nothing worked. Smashed my 2nd favorite coffee mug. Still
didn't work.
I'm going to pull the #14 LG/WH (L20) off headlight stud P and put it on a relay with the accessory switch. This way when the truck is off and I forget to turn the switch off the running lights wont kill my battery.
This should work?

 

Did you actually pull the fuses and replace them? I had headlights and no running lights recently, I too am on relays....did a quick visual on the fuses and they looked fine, so replaced my headlight switch....problem didn't change. So went back and actually pulled the fuse and found it was burned out down low near the spade connection....couldn't see it from a quick visual check. Tossed in a new fuse and everything started working again.

 

Fuse panel above brake pedal tends to melt in trucks with lights Not on separate relays. Turn the fuse panel over and look for melted plastic and burned wires.

 

Yep turns out I pulled the wrong fuse.
Change the right fuse this morning. All back to normal.
thanks

 

I just had this problem, it was the horn fuse. Park lights would not work on the park light setting on the head light switch. They would come on in a sweet spot past the park light setting on the head light switch but would not stay on when the head lights were on. When I bought an aftermarket head light switch they would not come on at all. I chased this for 2 months.

 

Glad you fixed it. We have had problems at work with cheap fuses preventing lights and accessories from working as well.