'90 300 SEL: All instruments lights go out
 

The instruments panel lights either are all on or all off. Lately mostly off.

I pulled the instrument panel out of the dashboard and while looking at the front of the panel, there is a small square box in the bottom left-hand side (it has one screw in it). When I squeeze this box or flick it, all of the instrument panel lights come on for a brief time. Then after some time, all the lights go out.

Anyone know what that is? If you had the instrument panel in, it in the direction of behind the left button that resets your mileage trip ( but I don't thing this box has anything to do with it).

In any event I would like to have my instrument panel lights! It's dangerous driving in the dark.

Any ideas? Any ideas what would make the instrument panels light flickers on and off? And now they are all mostly off.

Also, another clue, the lights for the heater controls and the window switches all go out in tandem as well.

i don't know if it is a coincidence, when i pulled the instrument panel out, i squeezed the item on the back left of it and the lights came back on for a short time.

I think what I am pressing in the "light control relay".

I don't think there's a lighting relay behind the cluster, it's under the hood together with the other fuses and relays. Sounds like what you're describing is the rheostat (potentiometer) that brightens and dims the interior gauge lights. If it's still the original pot and it's never had any TV tuner or similar electronic spray to clean it up, it's getting dirty and then it doesn't make good contact anymore. Result: dash and console lights flicker or are dim or disappear on you all at the same time. Not a difficult DIY, especially if you've already had the cluster out of the dash, and it's not big $ either.

Like Cal suggested
 

A little EPC (Electrical Parts Cleaner) and then a dab or two of WD40
on the Spring and Lever.

That's the dimmer for the lights. Remove the screw holding it on, and pluck it out. Try spraying it with contact cleaner. The EPC stuff is okay, I personally prefer DeOxit by Caig.

If that doesn't fix the issue, you need a new dimmer. I have one I pulled from a junkyard if you need......

One last thing regarding contact cleaners - they are not all made equal. A lot of them contain no lubricants in them, and as a result they will clean out not only the dirt contaminating your potentiometer, but also the grease lubricating it. If the knob feels all crunchy and scratchy afterwards, you'll know this has happened.

There are two ways to deal with this. The first is to actually open it up and replace the grease which got washed away by the solvent. The second is to use a contact cleaner that contains lubricants. Neither EPC nor DeOxit contain lubricants of any real viscosity.

A good compromise is to use a contact cleaner that contains silicones. You may have to use quite a bit of it before the silicones build up enough inside the potentiometer to have any effect.

Either way, make sure the pot is lubed. If it isn't, the wiper will eventually chew through the trace on the pad and you'll have to replace the whole shebang.

Wirewound pots are different. They typically do not require lubrication on anything other than the shaft. I think the dash light pot might be wirewound, based on its physical size, though I'm not 100% sure because I've never opened one up. If this is the case, then lubing it isn't as big an issue.

On second thought, the dash light pot probably isn't wirewound because wirewound pots typically don't have the issue you're having. They also 'feel' different than normal pots because you are dragging the wiper across wires and you feel the bumps......

yes, it is the rheostat. amazing they want $85 for it.

i pulled it out and put it back it. interestingly the light go out when you tighten the screw really tight, but when loosen it comes on. so i put the rheostat back on but not as tight. let's see how long it lasts.

the contacts looked clean.

thanks guys. this has bothered me for months.