Electrical Instrument Panel Light Dimmer Switch

alchemist

New Member
Jul 14, 2019
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north carolina
All of a sudden, the instrument panel lights went out last night on my 1991 LX Hatchback. Fuse is fine, and the overhead light still works. I've seen carbon pitting on some of the all in one light switches (and have fixed them), so i removed this one. It has two steel coil style resistor wires wrapped around a plastic shaft. There is one on the top and bottom of a gear drive wheel, and there are two 'points' one on top and one on the bottom, each of which contact the resistors.

I proceeded to use a small cleaning wheel (Dremel) to clean up both the coil wires (weren't all that bad). The points i cleaned up with a small ignition file, and there were also two buttons, again one on top and the other on the bottom, that were at the 'end' of the travel where the overhead/dome light engaged. I cleaned up each button (one was copper colored the other more silver color) as well. Put some D5 Deoxit on the whole thing.

Now, I actually get dash/instrument panel lights full, but in a very very small area of travel, right next to where the overhead light engages. It's easy to get both overhead dome light AND the instrument panel lights on at same time, but getting just the instrument panel lights on without the dome light is tricky. You have to nudge the dial to the left ever so slightly away from the full right setting. But go a little too far and the instrument panel lights go out altogether. The 'fade out' no longer works.

Something is still wrong, obviously. Would anyone have any advice? There appears to be a small resistor inside the unit that you basically can't get to without tearing the thing apart (but i'm thinking about it!). Betting it is bad.

Has anyone rebuilt one of these fully?

Thanks,
Robert Tilton
 
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The following are diagrams courtesy of Tmoss & Stang&2birds
mustangFoxLights-Radio_diag.gif


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.


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The same thing happened to mine years ago. Seems to be a common problem. After taking a meter to my switch I assumed the rheostat coil was bad somewhere under that green adhesive. That green adhesive crumbled and left a powdery mess so I tossed mine and got a new one. Sometime in the 90s Ford redesigned the switch. The newer design uses a contact pad and wiper that slides across the pad. That 'resistor' you see is probably the thermal fuse.

Panel Dimmer.jpg
 
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The same thing happened to mine years ago. Seems to be a common problem. After taking a meter to my switch I assumed the rheostat coil was bad somewhere under that green adhesive. That green adhesive crumbled and left a powdery mess so I tossed mine and got a new one. Sometime in the 90s Ford redesigned the switch. The newer design uses a contact pad and wiper that slides across the pad. That 'resistor' you see is probably the thermal fuse.

Panel Dimmer.jpg
Which dimmer is the early model and which dimmer is the later model?