Dashboard Illumination W123

[Bob S.]

I bought this car recently and since it now gets darker outside earlier I realized the dashboard lights arent working. The only illumination that I see is the trans shifter which of course helps but I need to know if it is a common problem that can easily be fixed. Help ! Thanks

[Ken300D]

One of the knobs below the meters is a potentiometer control that adjusts the dash lights from dim to bright. They are of poor quality. Try repeatedly turning the pot back and forth to get the lights on. With my '82 300D, there are only about three "live" spots across the whole range of the control - so I left it on the brightest and now never touch it.

Ken300D

[Bob S.]

Thanks I hope my problem is that simple !

my pot doesn't even work. thankfully it's stuck on the brightest setting (which isn't too bright anyway).

if it ain't the pot, then u might have to look at taking out the dash and checking out the 2 dashboard bulbs.

not a tough job, just gotta be careful when u try to "hook" out the dash.

Yes indeed, those potentiometers give trouble sometimes. I really don't understand how they can possibly burn out since the dash lights are so dim you could probably measure the current in microAmps.

Since the max setting isn't bright enough anyway, I just solder a jumper across the two copper strips on the back of the potentiometer, to give it a solidly reliable max bright.

If any of the other instrument panel lights besides the instrument cluster illumination itself are working, then the pot is making contact, in which case, yes it probably needs illumination bulbs in the top of the instrument cluster.

BTW, you don't need hooks to remove the 123 instrument cluster, simply remove the three trim pieces from the bottom of the dash, behind which are three phillips screws, remove them and the two phillips headed plastic retainers at the bottom of the lower panel cover and lower the cover, don't remove it, it's a hassle to put back in place. With the cover lowered reach behind the instrument cluster and simply push it toward the steering wheel. Occasionally it will try to hang on the plastic that surrounds it.

Once you have pushed the cluster forward far enough, you probably want to take it the rest of the way out and do the instrument bulbs or potentiometer work on the workbench. To get it completely out, disconnect the master electrical connector to the left of the speedometer, then using a 13MM open end as back up and a 10MM open end on the oil pressure line remove it, then remove the thumbscrew for the speedometer cable. There will be three more wires at the lower right of the cluster, pay close attention where they go, then remove them. The instrument cluster is now free.

Good luck,

Larry,

The disgusting thing I realized while reading your post was that I've pulled my cluster out of the dash so many times I was mouthing the words along with you! And I have to pull the dash again because one or more of my vacuum switches behind the console has died and leaks enough to keep the ACC from coming on anymore. I'm really getting tired of my 1980 300D!

someguyfromMaryland

SomeGuyfromMaryland,

I understand this frustration, it comes from taking the same part off repeatedly and not getting everything taken care of. Luckily, the instrument cluster in these cars is very easy to remove.

If you will keep up your perserverence, I believe you will reach a point where you're driving down the road one day and it will occur to you that you haven't had the dash apart in a long, long time. These kinds of problems come in cycles, regardless of what car you're driving.

Hang in there,

[jcd]

I tried the approach below on my 1977 300D. This was after replacing the bulbs and the potentiometer. This is either a creative or "you must be nuts" approach, but it worked. Not sure if you have the same set-up, but if you hate dim instrument lights as much as I do give it a try.

**************************

Remove the instrument panel. Remove all of the gauges and clean them and clean the inside. I just used H2O and paper towels.

I also cleaned the plastic "prism" that directs the light from the bulbs to the light diffusers that are in the front, nearest the driver, of the instrument panel. Again this was with H2O.

I noticed that the diffusers were a dull "yellow". My sense that the plastic had weathered or degraded. They were "welded in" via heated plastic tabs so replacement appears out of the question. In desperation, I applied some white flat paint to the diffusers, the idea being a brighter surface.

It worked. I took a steady hand and a small brush, but the instrument panel lights are much brighter.

JCD

jcd,

Thanks, that's a great tip! I wish I had read this before I took the cluster out of my daughter's car this weekend. It stands to reason, the reflector/reflection is everything in a headlight, why not the dash lights too?

You learn something new every day on mercedesshop.

[jcd]

Larry,

Even with this tip, I am still way in the hole as it relates to offering advice. Happy to help.

By the way, the heat on the 300D works great, with your help. It went from nothing to a real toenail melter.

Warmly,

JCD