I've searched the forum and found some threads like this, but no one seems to post a solution when it's found, soooooo....

1994 F150. Parking lights/instrument lights stay on when turned off. All bulbs seem to work. Pulling fuse 8 makes them turn off, and work normally! Unfortunately, this fuse powers my speedometer, chimes, cargo lights, which all seem to work fine.

Strange additional info: When they're on (when they should be off) the instrument panel dimmer will dim the parking lights! (but not the instrument lights)

Already replaced the headlamp switch, no help.


So whaddaya think, guys?

 

If you already replaced the switch and that didn't fix the problem, I'd check out the wiring for shorts downstream of the switch. The instrument panel illumination is getting voltage after the switch somehow, keeping them on regardless of the switch's position. Because the instrument illumination wiring goes all over behind the dash, a short anywhere could make the whole circuit hot and illuminate the dash. The wires in question should be blue with a red stripe. But since you said you can still dim the lights with the switch when it should be off, I'd start your search in the headlight connector itself. I don't have a handy explanation off the top of my head for why the parking lights dim, but shorts cause crazy things (so do bad grounds). I've seen the headlight connectors burn out before. They take a lot of heat.

 

I agree, you have a hot wire getting against a blue/red behind the dash. This would put 12 volts on all the dash lights, which would explain why they won't dim. This 12 volts feeding backwards through the headlight dimmer, and then backwards to the running light circuit, also explains why the running lights will dim. The power feed/fuse for the running lights also serves the circuit for the instrument lights.

The first place I would suspect a problem is a stereo or radio, or any place that something aftermarket has been installed, and the possibility of sloppy wiring or wiring mistakes exist. The blue/red instrument wire does go to the radio, and the radio does have hot wires going to it.

 

Thanks for the responses, guys.

Today I found a wire (green) at a connector under the dash. It is totally melted. It goes to the overhead in-cab light. It is melted right to where it connects to the light fixture, so I imagine that shorted somehow. It also goes up into the dash behind the instrument panel.

The whole length of this wire is melted. Haven't got into the dash yet, but I would say you guys are right that it has melted into the blue/red somewhere.

I am out of time for this project right now, but I'll let you know what happens.

Again, thanks!

 

OK, guys!

As I told you, the green/yellow wire was melted from a connector under the dash to the ceiling interior light. After pulling the front of my dash apart, I can see it is NOT melted at the headlight switch, but IS melted right to the fuse box. Unfortunately, I really can't get to the wiring harness behind the fuse box.

I want to cut the wire off at the fuse box, as I agree the green/yellow must be melted to the blue/red somewhere behind the dash. I would then run a replacement wire for the green/yellow.

This fuse runs several things, tho. Where does the one green/yellow coming from the fusebox split to go to the other things it runs? If I knew this I could run a new wire to power those things, AND continue to the overhead light. I can't follow it cuz I just can't get in the dash far enough!

TIA!

 

The lightgreen/yellow powers all the courtesy lamps. I am not sure exactly how the wire is run, but it goes to the headlight switch(so you can twist the **** and turn the courtesy lamps on) and goes to both door switches. It also goes to the glove box switch, vanity mirrors and map lights. On some trucks it also goes to the outside power mirrors.

 

Thanks Dave!

I plan to get into this on the weekend.
My other concern is that the fuse the green/yellow wire goes to (#8) also powers the speedometer. The back of the fuse box is hard to see, I could only pull it forward about an inch. But there is only one (melted!) green/yellow wire coming from that fuse, so I'd need to know where it splits to go to the speedometer so I could make sure that still gets power when I'm rewiring.

If anyones interested in WHY the wire melted, turns out the fuse is a 30 amp. Calls for a 15..... Seems to have shorted in the courtesy/dome lamp where the screw that goes thru the hot wire somehow grounded thru the plastic sheath thingy.

I might start checking fuses when I buy a used truck!

Paul

 

That's always a good idea; when I bought my '79 all the fuses in it were blown and wrapped in aluminum foil. It's a pretty important thing to check because you never know what someone may have stuck in there in the past.

 

Yikes, what a job!

Never actually found where the green/yellow melted into the blue/red. It had to be in the dash behind the fuse box where I just couldn't get to.

So I cut the green/yellow from the fuse box and ran a new wire to the head light switch, the speedometer, and all the way to the dome light.

The green/yellow was melted thru its plastic the whole length, and even thru the taped harness. Amazing there wasn't a fire!

Anyhow, everything works now, thanks for the help!

Paul