Hi there. I recently acquired a 1984 300D and noticed the dash lights were very dim. I ordered LED's to fix that problem but at the same time I noticed all the lights in the center (ie. climate control, etc.) were not working. I thought maybe it had something to do with the dimmer but I just took the instrument cluster out and noticed the dimmer had been jumped with a soldered wire. Which after research seems fine. I don't mind not having a dimmer.
Any thoughts why this is happening and how to troubleshoot? Thanks

The lights for the climate control and the sunroof/antennae buttons all come from one source, kind of.

Behind the climate control push-button unit, there is a hub with a few fiberoptic cables. The hub gets one bulb and there's a cable for each button at the top of the console. The CCU gets its own series of 5 light bulbs that plug directly into the back of the unit. You'll need to remove the CCU in order to replace or inspect any of these. There should be plenty of instructions on the site for removing the CCU.

Also, since I'm doing this exact service myself right now, it may be worth it to mention to you: the lights in the window switches in the center console are inside the buttons, not backlit. If either/both of those don't light up, you can replace the entire switch assemblies for really cheap.

It should be noted as stated the window switches have their own internal lights. Some after market switches that were not made by Mercedes do not have internal lights.

I have taken the CCU out and the bulbs look to be ok? (Although they are so tiny it is hard to tell???) If one is out will the entire series not light up? Also in doing research on this I have read that the hazard light button should also be lit? It lights up when I push it on but is not lit when not engaged?

Doh! That's a bummer to hear... The ones I bought (not yet arrived) were cheap aftermarket. I guess I'll see when they show up. Was only replacing because my PS switch lights were dead


Did you turn the lights on while looking? If the bulbs are good, it'll be obvious. The lights will all work independently of each other, so one being out will not keep the rest off. Lastly, the hazard is lit but if I'm not mistaken, only when the button is depressed to turn the hazard lights on.

yes I tried with the lights on. None of them behind the CCU turn on. Hazard does turn on when depressed but not when it is in the off position.

Update: I just put in the LED's and all the dash lights look great. Still dark on all the console lights (ie. spider and CCU)??? Can anyone tell me where or how to trouble shoot this? Thanks

That spider I was fascinated with, goes to show why Mercedes was able to charge $30K for these cars way back then!

In my case it was a question of the grounds, MB love to run a separate ground for almost everything, there is a snake pit of grounds on the steering wheel column mount. Sadly to chase it down you'll probably have to pull the center console out and physically chase down the wires.

In another question, what LED's did you use in the dash, I tried to do that but I still have a functional dimmer, and every time they would cause traces in the board to blow out.

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

I do not have a dimmer. There is a wire soldered on the back between the posts where the dimmer used to be.

Yeah, that was the most common "fix" for when the dimmers went bad. But, I guess at least you can use LED's. Still curious what LED's you used.

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

I used T5 leds. I just had to modify the wire that came on them. As far as the CCU/switches lights not lighting, I have the center console all apart but to be honest I don't know my next steps to troubleshoot the wires? Can anyone help me out on that? Thanks

Do you have a test light? Find a good known ground for the test light, and touch on a connector, or if you have to, poke into a wire with the sharp end, while the lights and ignition are on. If your test light lights up, it tells you the ground is bad to your lights.

If it doesn't light up, then you know you don't have power going to them, chase the wires back till you find where they are disconnected or broken or shorted out.

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

I did a test light on the wires. Neither one of them seems to have power. The wires seem connected as far back as I can chase them. Any other thoughts from anyone? This is frustrating! Thanks