Odometer Gears Changed now no Dash Illumination - Mercedes-Benz Forum
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post #1 of 11 (permalink) Old 06-08-2018, 05:36 PM Thread Starter
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Exclamation Odometer Gears Changed now no Dash Illumination

Yesterday I changed my odometer gears because they had stopped registering mileage and found they were very brittle at 335,215. Now I put everything back together but for some reason there is no illumination in the dash area. So I cannot see anything (gas level, oil pressure, speed, etc.) when i'm driving at night. I posted some pictures and if anyone can indicate where I need to start my diagnosis that would be very helpful. Thanks.
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post #2 of 11 (permalink) Old 06-09-2018, 01:49 AM
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One problem I've often experienced was the cluster light rheostat corroding and causing an intermittent connection. It's held on by a screw behind the dimmer knob and if you remove it you can jump the two leads to provide full current and bypass the rheostat. I've never felt the need to dim the interior lights anyway. Worth checking out
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post #3 of 11 (permalink) Old 06-09-2018, 06:18 AM
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Great idea SpartanPete, I also have this problem, how would you jump the leads?
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post #4 of 11 (permalink) Old 06-09-2018, 09:22 AM Thread Starter
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Quote:
Originally Posted by SpartanPete View Post
One problem I've often experienced was the cluster light rheostat corroding and causing an intermittent connection. It's held on by a screw behind the dimmer knob and if you remove it you can jump the two leads to provide full current and bypass the rheostat. I've never felt the need to dim the interior lights anyway. Worth checking out
Thanks much SpartanPete. I'll have to look more into it. Thanks again.
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post #5 of 11 (permalink) Old 06-09-2018, 09:39 AM
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Once you remove the rheostat you'll see the two leads underneath. All you have to do is run a short wire between them. You can solder the wire on but what I found was that the female pins in factory connectors fit almost perfectly over the leads. I had some spare connectors lying around so I took them apart and cut two of the female ends off and joined them together with a butt connector and then jumped the leads with that.
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post #6 of 11 (permalink) Old 06-09-2018, 09:50 AM
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If I remember correctly I took apart an instrument cluster connector and used those pins because they're smaller. I think the pins from my picture are too big but it's just a reference
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post #7 of 11 (permalink) Old 06-09-2018, 02:41 PM
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It's nearly always that rheostat.

'86 420SE
'90 420SEC


Daily transport 9spd Giant DH Comp downhill bike
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post #8 of 11 (permalink) Old 06-12-2019, 08:50 AM
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In case anyone is still interested, I posted steps I used to fix a dimmer:

https://www.benzworld.org/forums/w12...l-guage-2.html
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post #9 of 11 (permalink) Old 06-12-2019, 10:00 AM
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Quote:
Originally Posted by SpartanPete View Post
One problem I've often experienced was the cluster light rheostat corroding and causing an intermittent connection. It's held on by a screw behind the dimmer knob and if you remove it you can jump the two leads to provide full current and bypass the rheostat. I've never felt the need to dim the interior lights anyway. Worth checking out
That's what I did. Worked like a charm. Even at max brightness it's not too bright so therefore a perfect solution.
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post #10 of 11 (permalink) Old 06-14-2019, 05:58 PM
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Going to hijack this a little. A while ago put the aluminum foil in the two dash background light channels and put some new LED replacement bulbs in. Really made a difference and could adjust the brightness with the reostat. Fast forward a couple of months where I had the dash out mant times and removed both the vacuum/oill pressure dash module along with the speedo section. I probablly took them apart 10 times. (I was trying to repair the oil level indicator light. So after putting it back together I found the dash background lights now do not work. I checked the fuse, good, I checked the plug on the back of the dash, good. I checked both sides of the reostat. Both good. I checked where the bulb is powered and its very weak. I tried putting back the normal bulbs and no change. So I have no dash backlights ! My question is how does the center piece of the dash where the background bulbs get its power from the module with the round plug with all the pins? There is no obvious connection between the two sections, well only a bar which I assume is ground strap. I surmise there is a connection that is there but is weak. Any ideas? I am almost to the point of wiring the bulbs directly from the rheostat to the bulb but that is a last resort.
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