Inside Lights and the dimmer rheostat - PeachParts Mercedes-Benz Forum

rmmagow · #1 10-15-2003, 07:48 PM

The dash lights on my 123 are vary dim and moving the rheostat I can feel a sort of crunchyness and the lights basically go off. How difficult is the rheostat to replace after the panel is out. Does the panel's oil pressure guage use actual oil or is the pressure derived from something under the hood, meaning, am I gonna get oil all over the place trying to disconnect this panel. Has anyone used the dash light improvement kit from Mercedes Source.com and is it worth the money to upgrade the dimmish guage lights?
Thanks for any and all advice.

#2 10-15-2003, 08:09 PM

Never used that kit, but I solved the rheostat failure by removing the rheostat and wiring the two posts together. Easy fix. Lots of light now. Just pop the dash out. I usually just reach up behnd and shove it out. Of course the correct way is to use a hook tool to pull it out from the front. Either way it comes out easily.
Some have found you can get even more light by cleaning the instrument cluster carefully. Gets dark with age.
The 123 used an oil pressure line up til 79 I believe. Then went to an electic sending unit. Might be off by a year there. Have an 81 123 parts car with electic sending unit and a 78 with a plastic oil line to the dash.

Toblin · #3 10-15-2003, 08:14 PM

Old Deis,

I have the same weak dash light prob. Could you be more specific as to how to get at the rheostat? Thanks!

81Wagon · #4 10-15-2003, 08:16 PM

I used the kit - I'd say go for it. It's quite simple. Push the cluster out form underneath (in my case trying the "correct" way only succeeded in scratching the crap out of the sides of the cluster - it was fitted tightly because the dash has warped) and carefully unplug/unscrew everything to get the cluster fully out. I have an 81 123 and it's still got the direct oil pressure line, but it didn't even drip when I disconnected it (just don't start the car with it unscrewed!).

The rheostat is at the back of the cluster and is simple to remove and replace (one or two screws). The brightness and color of the new lights are much better than the old, you'll love it!

#5 10-15-2003, 08:20 PM

Pop the dash out and you can get to it. It is right behind that knob that dims the dash.
If you do not wish to use the dimmer, then remove the porcelan square assembly from the rear of the instrument cluster. Takes a philips #2 screwdriver to take it off.
Then either replace it., I believe I have seen them here, of I just used a wire with two round things from a Radio Shack kit and pushed them on the two metal posts that will remain after the other stuff is removed. Like I said, not hard to do.

bjcsc · #6 10-15-2003, 09:46 PM

I do not think my dash lights are too dim, but I always read where everyone else seems to. Same experience with my US headlights - no problem - plenty of light. At night on road trips I often dim my dash lights as they are too bright. What gives?

lrg · #7 10-15-2003, 11:15 PM

I used the bulbs from that kit on my 123 and later had a problem with heat melting the clear plastic that "conducts" the light to the front of the panel. Before you put in the new bulbs try another fix. Remove the panel completely (by the way 81Wagon is right, the oil line won't leak more than a drop unless you have pressure). You'll need to remove the speedo cable, oil line, and electrical connector at the back of the panel to get it free. You can access them by pulling the instrument panel out as far as you can and slipping your hand in behind. Do the oil line last. Once off you can easily get at the rheostat to solder a jumper or clean it up so it works better. The best fix is to remove the left and right instrument clusters (tach on one side, gauge set on the other) so you can get at the little "compartments" behind the two bulbs that light the whole panel. I found mine had both turned brown (they are supposed to be white) and painted them glossy white. This made a BIG difference. While you are at it replace the stock bulbs with new ones since those somehow get darker too. Chances are good this will solve your problem. I can't tell for sure that the "upgrade" blue bulbs caused my melting problem but I can tell you that after installing them the light was better at first but then got much worse. I eventually had to buy a new(used) cluster and applied the above fix. Since then the light is much better but still not as good as on my 124. I think MBZ improved this design in later models.

Old Deis,
Not sure about all the 123s but my '85 has the oil line to the gauge. It must be that some were electric and some mechanical.
Go figure.

81Wagon · #8 10-15-2003, 11:35 PM

If I remember correctly the new lights from that kit are lower wattage than the stock ones (maybe they were the same). Seems like they shouldn't really get any hotter (but I'm no lighting expert). I haven't had any problems yet, but it's only been a couple of weeks. I'm going to pull the cluster again to repaint the needles soon, so I'll check for any evidence of overheating in there.

Speaking of the electric vs. "mechanical" oil gauge... I thought the 123's had mechanical speedos, but mine just has a screw-in, one-pronged electric plug...?