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1977 Mercedes-Benz 300D(non-turbo)
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101 Posts
Discussion Starter #1
I have removed my cluster looking for a short and discovered why(i think) my gauge cluster lights dont work. The little spring in the dimmer switch was all twisted. Can this be fixed or do i have to order a new one? Can i put the cluster back in without it so can drive the car until a new one arrives? The dash lights have never worked since i bought the car but strangely the shifter light has?
Thanks in advance!
 

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500 Posts
The "spring" in the dimmer switch should look like, well, a coiled spring. If not, that probably is your problem. That switch is a common part to fail on these cars. Many people simply solder a jumper wire between the terminals to bypass it and run the lights at full illumination. The lights aren't very bright to start with. You can definitely reinstall the cluster as the dimmer is a non essential part, except at night if you want to see the gauges. You can try to fix it if you want to, but I think they are relatively cheap new.

P.S. I don't think the shifter light is connected to the dimmer. All lights in the cluster, climate control, and upper center rocker switches are.
 

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1979 240D 4 spd
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320 Posts
I had this issue and it turned out to be the "dimmer switch." The switch is called a rheostat. KCM is right about a lot of people jumping the two brass strips on the top of it. Also, spray contact cleaner on that spring and work the "spinner." It should do the trick.. But, That worked with mine for a while until I took the cluster out to mess with the clock, then it didn't work after that. What I did to fix it was take the back of the cluster apart. You'll see the other side of that board that the rheostat goes into is an integrated circuit board. I soldered a wire between the backside of the two pins the rheostat engages with. It was quite simple (if you have a soldering gun of course) and has worked since. I hope that this helps.

The lights ARE quite dim... but certainly better than nothing.
 

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1977 Mercedes-Benz 300D(non-turbo)
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101 Posts
Discussion Starter #4
Thank you both for your input. Dont have a soldering iron so i tried ti tape a small wire to bridge them just to see if it would work...it didnt. Im just going to order a new switch. If THAT doesnt work then i have no clue. Thanks again y'all.
 

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1977 Mercedes-Benz 300D(non-turbo)
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101 Posts
Discussion Starter #5
HOLY COW!

So...Nevermind about ordering a new switch! the dealer was the only one who could order it and i swear he said $180...maybe $118 but as soon as i heard "a hundred" i said ok...thanks very much. looks like im buying a soldering iron on the way to work!
 

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82 300D
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10 Posts
I pulled out the cluster on my 300D today and soldered in a jumper to defeat the dimmer, and just as I expected all of the related dash lights now work. I also installed L.E.D.s for the cluster illumination and super glued the little chromy things back onto the hubs of the guage needles. I probably spent way too much time on the whole project but I am very fussy about fixing everything that I can before I put a dashboard back together. Defeating the rheostat is an easy job and in my humble opinion so is removing the cluster, despite what some members here say. Tool up and dig in!
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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10,152 Posts
So...Nevermind about ordering a new switch! the dealer was the only one who could order it and i swear he said $180...maybe $118 but as soon as i heard "a hundred" i said ok...thanks very much. looks like im buying a soldering iron on the way to work!
Yeah, not cheap, Your Parts Search Returned 1 Part(s)

Many folks have success with simply soldering it, good luck.
 

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1979 240D 4 spd
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320 Posts
Agreed with Rmac - Definitely not cheap. I'd definitely buy yourself a soldering gun. They are super useful after all. Solder up and I'm fairly confident your troubles will go away.
 

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1977 Mercedes-Benz 300D(non-turbo)
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101 Posts
Discussion Starter #11
Check the fuses, jump the switch and check the bulbs.
While i had it out, I compleatly disassembled the entire thing. All bulbs were fine and so were the fuses. Ill jump the switch tomorrow.....tied one on lastnight and dont feel like doing much today! :)
 

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1984 300D Turbo, 2003 C240, 2011 E350
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31 Posts
I pulled out the cluster on my 300D today and soldered in a jumper to defeat the dimmer, and just as I expected all of the related dash lights now work. I also installed L.E.D.s for the cluster illumination and super glued the little chromy things back onto the hubs of the guage needles. I probably spent way too much time on the whole project but I am very fussy about fixing everything that I can before I put a dashboard back together. Defeating the rheostat is an easy job and in my humble opinion so is removing the cluster, despite what some members here say. Tool up and dig in!
Would you happen to have a picture of which two points on the rheostat you soldered a jumper to permanently defeat the dimmer function? Anyone?
 

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Man you should take a close look for the reason that sometimes just the switch can be replaced and you don't give the model/yr/make but you may be able to go to a U pull auto wreckers and pull the whole cluster which cause you for about 25-75 bucks only.

Good Luck and I hope it will help you. Anyway the dimmer switch also controls the interior lights and if their still functioning you may include more then just a switch concern.:thumbsup:
 
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