Instrument cluster power - Mercedes-Benz Forum
 
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post #1 of 7 (permalink) Old 06-21-2019, 11:27 AM Thread Starter
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Instrument cluster power

I have had the cluster out zillions of times and have also taken it apart into its three main components many times as well. White faces etc. well lately I can’t get the instrument cluster lights to work. Yes checked the fuse its good. The rheostat too. It has power on both sides of that and even tried a different one. The 15 pin has power too. The middle square plug also has power to some of the pins and this is the one right behind the speedo. So how does the middle section get power from the rheostat? There is really no jumper from one section to the middle section where the backlights are so I wonder how they do it. I must be missing some connection that is faulty. Does the rheostat feed power back into the 15 pin plug and then they route it to the middle plug? Is it the circuits in the board? As an aside the speedo will work sometimes some not, but I think that is a separate issue unless there are resistors in the backlight power circuit that are going bad. I do have led bulbs in it now for the backlight since they are brighter but have also switched back to incandescent just to test. No change.

I do not want to get a new speedo section since I have already had the odometer fixed and also put white faces on. Any suggestions? At one point I was contemplating running a wire from the rheostat directly to the backlight bulbs. Might still do that. Any input is helpful

Last edited by Stutz; 06-21-2019 at 11:31 AM.
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post #2 of 7 (permalink) Old 06-21-2019, 01:04 PM
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Hey Stutz,

Reading your query here, I see no mention of ground supply..

Here is the diagram for your instrument backlights..

I wonder if this might shed light?
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post #3 of 7 (permalink) Old 06-21-2019, 02:05 PM Thread Starter
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I checked all the grounds behind the cluster. All were good and tight
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post #4 of 7 (permalink) Old 06-21-2019, 04:34 PM
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Dog with a favorite bone here,

but what happens if voltage is applied to x1....?

That should light the instrument backlights.

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post #5 of 7 (permalink) Old 06-22-2019, 11:24 AM Thread Starter
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Have power at x1. I think its supposed to come from pin 15 on the round plug on the back of the cluster. I have full power (x1) on both sides of the rheostat. How does the power get from there to the lights? Remember there are different sections and seemingly no connections between the two.
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post #6 of 7 (permalink) Old 06-22-2019, 12:55 PM Thread Starter
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Ok, figured it out. Foolish on my part but.... when I had the cluster out those zillion times I was trying to change the bulbs to LED. For some reason I did not notice one was a fuse and not a bulb. As such I simply put a bulb in that socket. So nothing was correct. Attached is a picture of a cluster from an 88 with the correct position for the fuse holder. Its the one in red. Now to work on the speedo.
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post #7 of 7 (permalink) Old 06-23-2019, 02:01 AM
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That's great!

Glad it was a simple solution..


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