Guys I just bought used 99 f-250 4x4 5.4L crew cab. Tonight when I was driving it, all of a sudden the instrument panel lights just started dimming until they were out. I rolled dimmer switch both ways, even to the point the lights in the cab would turn on but the instrument cluster was still out. I would drive along and roll the dimmer switch and the instrument cluster would start to light up, not to full power but just barely. It strange when I first start the drive, the instrument panel lights are bright. The radio works fine when the lights go down, the lights outside is fine and brake lights are fine as well. I looked at all the fuses and did not see any out, otherwise the lights would have never worked, but I'm wondering if threes some relay or fuse that's going bad that when it heats up its causing the instrument panel to dim down. Anyone has any suggestions as to what I else I can try. Also I did keep the fuse panel open and try and jiggle some of the fuses when the instrument panel dimmed down on its own but it was hit or miss as to whether that made a difference. Any advice would be appreciated. I did notice one time tapping by the dimmer did brighten the instrument panel lights up a bit , but that did not always work.

 

I would think the previous owner used one of the crap add a fuses to that circuit, and stretched out the fuse slot for the instrument lights. This should be fuse #18, Central Junction Box ( cab fuse box ).

The other cause aside from Fuse #18 on, is from the Main headlamp switch. When in the park of head position, this feeds power to Fuse #18 in the CJB, so it could be a problem with the main headlamp switch as well as maybe the dimer switch.

Quick test

1. pull CJB fuse #18.
2. USe a meter to find which side has power when the main headlamp switch is in the park position.
3. Use one of the good add a fuses to power that side of the socket ( headlamp fuse ) and have the other side go to a male spade that you put into the dead side of Fuse slot #18.


-> This will illuminate the dash when you turn on the headlamps, removing the main headlamp switch from the equation. Make sure the male spade is in the slot tight.

If this cures the problem, you have an issue with the main headlamp switch.

By any chance, did the previous owner do the fog lamp switch modification so they could turn on the fog lamps without the headlamps on ?

Good luck, let us know what happens.