I have a 1991 F-150. About 2-3 weeks ago I was driving home and my marker lights shut off. I pulled over and pushed the switch back in and back out, but the headlights were the only thing that came on. The switch has two settings, one for markers, other for headlights. When i pull it out to the marker lights setting, nothing happens. When i pull it out to the headlights setting, only the headlights come on. I have to find the point between the two settings where both lights will come on as my dash illuminates with it. Since it's getting darker by the day and will start raining soon, i need to get this fixed. A new headlight switch didn't work, and wouldn't even have both come on so i stuck with the old one. My highbeams still work just fine also. I have started checking grounds but so far, no luck. My truck isn't even road safe right now and cops are starting to get suspicious. Please any info would be great, thank you.

 

im assuming you checked fuses already?

 

Yes. All fuses look good. On the back of the tan plug that fits into the headlight switch, the two red wire connectors had turned brown and expanded due to heat. Replaced those and still no luck.

 

Did you check the relay?

 

Haven't checked the relay yet

 

He doesn't have a relay.

Two separate circuits, one for headlights one for parking lights. Make sure you are getting power to both.

 

I'm pretty sure there's a relay. You wouldn't want to send all that current through the switch.

 

That's what they did, and that's why his wires were melted. No relay on '91.

 

I just googled looking for an answer and it seems you're right.

OP, if u have a volt meter u can check the contacts on the switch to see if the switch is delivering power. If so, your wire is probably burnt up somewhere between the switch and the lights.

And make sure you're getting power to the switch in the first place.

 

I already checked both the parking and headlight switch contacts and wires, they both have power.