My '88 F250 has the optional map light/dome light.
The dome light works correctly from the doors and the headlight switch, but I haven't figured out how to turn on the map lights with the switches on the light fixture.
Do they work by themselves with the key off?
Do they require headlights on?
What feeds them power?
The wiring diagram I have isn't much help as none is labeled and I'm having problems chasing the wires back to hot.
Surely someone knows ?

 

The slide switches should operate the map lights with ignition on or off, as that circuit is hot at all times. The bulbs may be burned out so I would suggest you check that. Also check all your fuses and circuit breakers. In order to check the bulbs the fixture will need to be removed by carefully releasing the tabs that hold the lens in place. Then remove the three phillips head screws that not only hold the fixture in place but also provide the path for the electrical current. At this point, you might also discover the screw providing the current path for the map lights may not be properly contacting the metal tab in its terminal end. If you would like to do an upgrade to the newer plastic frame lamp assembly they are a direct replacement and, due to their clearer lens, offer a better illumination.

dn.

 

OK, I checked the wiring. There's a GRN w/Yel coming to it and a Black w/Blu. Neither are hot. The dome lamp appears to work off the Black/Blu and works OK from the doors and the hdlt switch. The GRN/Y is not hot and the map light switches appear to connect the GRN/Y with the Black/Blu. According to the wiring diagram there's a diode involved but I don't see why.
The bulbs are good and the mounting screws appear to go where they should, one goes to ground, one to the clip for GRN/Y and one to the clip for Black/Blu.
The wiring diagram shows the dome lamp wiring goes to the fuel pump relay, but then it doesn't really show it.
What fuse feeds the GRN/Y ?

 

The map lights on my '89 F-150 only work with the parking or headlights on. Have you checked for power with the headlight switch on?

I replaced the dome light lens with a clear one and went with a LED bulb. Very bright inside the cab now.

 

^^That is what I remember(hardly ever use the map lights).

 

It makes sense they only work with the lights on - can't walk off and leave a drain on the battery that way.
OK, so I check the GRN/Yel lead to the fixture and it's not hot, not always and not with headlights on.
So I'm left with the original question - What fuse feeds the map lights ? Do I have a fuse problem or a wiring problem ?

 

Sounds similar to the problem im having except i havent gotten any of my interior lights to work at all. Mines a wiring problem so id guess yours could be to ? both my light wires coming off of the headlight switch have melted before i bought it and been very cheesily replaced.