1988 F250 7.5L Headlight Issues
 

I am having issues with head lights on a 1988 F-250 7.5L standard cab.

1) When I pull headlight switch all the way, head lights work, but not the taillights, front side markers, cab markers or dash lights.

2) If I push switch in slightly, the headlights go out and all lights listed above as well as warning sound for "lights on" work.

I replaced the switch, but I continue to have the same problem. Any thoughts on possible causes?

I could also use a more complete wiring diagram for my vehicle than the one I have in the Haynes manual. Any assistance on where to get a complete wiring, troubleshooting manual would be greatly appreciated.

When you replaced the switch did you inspect its harness connector?

They melt/burn/deform, you can buy a replacement pigtail if its found damaged.

Harness connector the switch plugs into looks good.

Did you look at the harness connector where the switch plugs in, if not and from the back or side it probably looked fine. Gotta look at it where the pins connect, the center of that area melts/deforms.

If you did and its good then you probably just gotta bum/china switch.

Thanks for the help. I'll take a closer look. Any ideas for a good source for the harness? I bought the switch from LMC, but I don't think they sell the harness.

Any ideas for a good source for the harness?

IIRC I got mine at napa, been a while though.

Problem with the melted connector is it deforms the switch pins once attached, I had very similar issues with mine. And no I didn't notice the connector was deformed first time I swapped out the switch, IIRC don't readily/easily see it from that angle while doing so.

Same thing for me, new switch same problem, when I took it back out to see what the deal was that is when I finally noticed, after several minutes of back probing testing circuits and scratching my head, that the connector was melted. Deformed pretty bad too, not far from burning down the truck by the looks of things. I was glad I did see it, liability only on that one.

Thanks.
 

Thanks again for the help. I have a new switch and hraness on order from NAPA. Will give update when installed.

This actually happened to me on my 1996 F150 XLT, turns out it was a blown fuse in the fuse box underneath and to the left of the steering wheel. Hope this helps.

Here's the schematics for the headlights and marker lamps.

http://i135.photobucket.com/albums/q...lt/PG048-2.jpg

http://i135.photobucket.com/albums/q...lt/PG051-2.jpg

Thanks for all the help!!!!!
 

It turned out to be a blown fuse. Never would have guessed a blown fuse would cause this problem. Thought it was the switch for sure. Now I have some spares from NAPA for future issues.

This is my first post and you guys gave me some great info. Hope I can return the favor in the future.

Good lookin out Jlynch2011, yea I was working under the assumption the fuse had been checked, nope shouldn't have done that.

1988 f250 light switch problem
 

What type of fuse was it i checked all the fuses and all looked good,was it in a different spot.

Thanks,
Mark