I have an 88 F350. The headlights and running lights come on just fine but when you turn them off the running lights stay on. I replaced the headlight switch and no luck its still doing the exact same thing. I dont have the owner manual so i dont know where to find the headlight relay or if there is something else I need to be looking at to make them shut off correctly. Please help...

 

I am assuming you are talking about the parking lights. There is not relay, the wiring is very very simple for these lights. The headlight switch gets power from it's fuse, and when you pull the light swithc **** out one click, then power is sent to the parking lights, when you pull the **** out all the way, power is sent to the parking lights and the heaklights.
Either something is going on inside that switch, or you have a short to power in the electrical somewhere.
From my understanding the parking lights ar on all the time right? Unplug the light switch and see if they go off.

 

If i do not disconnect the ground cable from the battery then yes, the parking lights and the running lights across the top of my truck stay on all the time. The headlight switch was just replaced yesterday, so it is brand new and if there is a short to the power in the electrical somewhere, I have no idea where to start to look for it. So I'm assuming that you're telling me I have to go through all the electrical going from the switch to the headlights and the running/parking lights.

 

Yea you are going to have a nice little electrical hunt on your hands. My ford wiring book for the 1988 model is at work right now, but for now my 1996 wiring book can help.
1) Try diconnecting the big connector mounted on the firewall (if you have on) on the driver's side (not the ones on the fender). With that diconected if the lights stay on then it is something outside of the cab (this can make it a little easier).
2) If it is outside the cab check your trailer wiring harness, disconnect the conectors at the rear bumper on the driver's side frame rail, if the lights go out then it is in the trailer harness after that conector If the front lights stay on and only the rears go out then it is something closer to the front or middle of the truck.
I have seen alot of the wiring harnesses on thoes older trucks rott out at the driver's front corner section, that would be my next check.

 

Something else to try is to pull the fuse for the lights, and since they should still be on, start pulling the other fuses one by one till the lights turn off. This will tell you what circuit they are drawing from, and may make it a little easier.

Do you have any aftermarket wiring on the truck, extra lights, plow or anything?
Where are you located?

 

Well I will try that tonight and let you know what I find out tomorrow. Thanks for the help.