w115 Electrical woes (instrument cluster lights?)

[Monomer]

instrument cluster lights on my 1976 300d are not working. Anyone have a schematic for a car this old?

[300SDog]

Ye dont need schematic - its always the dimmer switch. In all my years have never seen fully functional vintage MB dimmer switch. Cluster light dial switch is like a joke that nobody takes seriously. Ye just fiddle with it and be happy you've got instrument lights at all. Permanent solution is pull the rheostat switch and bypass it with solder weld blob, then reinstall.

[Kpmurphy]

Instrument cluster on a 115 I also have a question?
Does any one know wat the 2 alligagtor clips are doing on the back of the instrument cluster?
Kevin

[Mark DiSilvestro]

Originally Posted by Kpmurphy

Instrument cluster on a 115 I also have a question?
Does any one know wat the 2 alligagtor clips are doing on the back of the instrument cluster?
Kevin

Looks like someone already discarded the malfunctioning dash-light dimmer, and jumpered the connectors. The clips should be attached to the two pins sticking out of the circuit board. Are your dash-lights working?

Happy Motoring, Mark

[Kpmurphy]

Originally Posted by Mark DiSilvestro

Looks like someone already discarded the malfunctioning dash-light dimmer, and jumpered the connectors. The clips should be attached to the two pins sticking out of the circuit board. Are your dash-lights working?

Happy Motoring, Mark

Yes they are working
Thanks for the info
Kevin

[Monomer]

whats this dimmer switch everyones talking about?

[Mark DiSilvestro]

Originally Posted by Monomer

whats this dimmer switch everyones talking about?

There's two small round knobs on the bottom on the instrument cluster. One resets the trip-odometer. The other is connected to a rheostat (variable resisistor) on the back of the cluster that controls the brightness of the dash lighting. Usually the rheostat and it's rotating contact gets corroded. Sometimes you can spin the dimmer knob back & forth many times, and wear away enough of the corrosion to get the dash lights to work, at least at some point of the contact area. Or you can pull the cluster and replace the rheostat. Or repair it - involving removing the rheostat, prying off it's metal cover, cleaning up the contact areas, then reassembly. Or leave it off and rig some kind of jumper in it's place at the two rheostat contact pins on the cluster circuit-board, to bypass it, which will run the dashlights at full brightness.

Happy Motoring, Mark

[Monomer]

Originally Posted by Mark DiSilvestro

There's two small round knobs on the bottom on the instrument cluster. One resets the trip-odometer. The other is connected to a rheostat (variable resisistor) on the back of the cluster that controls the brightness of the dash lighting. Usually the rheostat and it's rotating contact gets corroded. Sometimes you can spin the dimmer knob back & forth many times, and wear away enough of the corrosion to get the dash lights to work, at least at some point of the contact area. Or you can pull the cluster and replace the rheostat. Or repair it - involving removing the rheostat, prying off it's metal cover, cleaning up the contact areas, then reassembly. Or leave it off and rig some kind of jumper in it's place at the two rheostat contact pins on the cluster circuit-board, to bypass it, which will run the dashlights at full brightness.

Happy Motoring, Mark

just what I needed, thanks!

[ja17]

The alligator clips are a very creative and cheap way of getting the dash lights to work again!

There are always at least two things made by VDO that are not working on a vintage Mercedes. Most likely are, tip odometer, dimmer switch, turn signal cancelation, cruise control amp, Etc. I am sure you guys can add to the list.

[e320talk]

I think I have the same problem. My car is a 2002 e320 wagon 4matic. The cluster lights for night time driving don't come on when the headlights are turned on. Changed bulbs and fuses but no change. The cluster dimming is controlled by two buttons on the left side of the cluster. Can I somehow bypass the dimmer on my instrument cluster? Thanks.

[Mark DiSilvestro]

Originally Posted by e320talk

I think I have the same problem. My car is a 2002 e320 wagon 4matic. The cluster lights for night time driving don't come on when the headlights are turned on. Changed bulbs and fuses but no change. The cluster dimming is controlled by two buttons on the left side of the cluster. Can I somehow bypass the dimmer on my instrument cluster? Thanks.

Unfortunately, since the 1970s, many automotive electrical systems have evolved from simple DIY-friendly electro-mechanical components, such as dimmer rheostats, to pushbuttons & microchips. I suspect your dimmer won't be easy to bypass.

Happy Motoring, Mark

[Monomer]

Originally Posted by Mark DiSilvestro

Unfortunately, since the 1970s, many automotive electrical systems have evolved from simple DIY-friendly electro-mechanical components, such as dimmer rheostats, to pushbuttons & microchips. I suspect your dimmer won't be easy to bypass.

Happy Motoring, Mark

no-one here at home gets why I like the older cars.



Lights are working, for the most part. Very dim, as if a few of the bulbs are out (ordered new ones from fastlane) How hard is it to pull the cluster? It sure does not look like any of the pull-out clusters I've had to deal with.

[Mark DiSilvestro]

Originally Posted by Monomer

no-one here at home gets why I like the older cars.



Lights are working, for the most part. Very dim, as if a few of the bulbs are out (ordered new ones from fastlane) How hard is it to pull the cluster? It sure does not look like any of the pull-out clusters I've had to deal with.

On the W114/115, the cluster is pressed into the dash hole. Unlike the earlier Benzes, there's no thumb-screw securing the cluster. Just a rubber gasket surrounding the cluster-housing that grips the inside of the hole. If you can't work the cluster loose by hand, you may have to fabricate some type of slim tool to get between the cluster and the dash, or try to get behind the dash and push it loose from behind. If you need to get the cluster out pretty far to reach the bulbs or dimmer, in addition to the speedometer cable, you'll need to disconnect the oil-guage line. Older W114/115s also had a mechanical temp-guage line to worry about, but I believe your 300D temp-guage is electric.

When it's time to reinstall the cluster, you may find the rubber gasket has dried or shrunk and no longer grips very well. In my '72 W114 250, I cut a strip of cardboard to insert between the gasket and cluster to make it fit tighter in the dash. Alternately, a few turns of electrical tape should also work here.

Happy Motoring, Mark

[Mike D]

The key thing to remember in Mark's post is the "between the gasket and cluster" ESPECIALLY regarding using electrical tape! It's a mess pulling out the cluster after the goo from the electrical tape melts and re-formulates between the gasket and the dash cut-out.

Alternately, the speedo cable is supposed to fit in a bracket down on the firewall which applies a retaining force to the cluster. By now either the cable has lost it's protective outer sheathing or the bracket has spread.

After you are sure the lights are working and all the gauges work use a "zip-tie" to keep the cable in the bracket.

[whunter]

This is now my daughters car.


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