Where does the guage cluster get ground from? - PeachParts Mercedes-Benz Forum

stephenc03 · #1 10-23-2008, 02:17 PM

I have a 85 300SD and I am wondering where the dash cluster gets ground. I posted a thread on here a few weeks ago about my fuel, oil pressure and temp all reading at there maximum reading. 85 300SD fuel,temp, and pressure guages not working!!

Today I went to the local pick and pull and bought a complete guage cluster and the board that it attaches to. It is still doing the same thing. I know I have a short somewhere or possibly not getting enough ground. There are four metal tabs that attach to the dash where the cluster seats into it...i dont see how the cluster would be able to recieve ground from these tabs. I tried wiggling the cluster to see if it was a simple contact and still nothing. I have checked the fuses and they are all fine. What should I do next?
-Stephen

curtludwig · #2 10-23-2008, 02:43 PM

Good question. I added a ground cable to the cluster on my '83 240D... I *think* that the ground comes through the wiring. I suspect on mine I've pulled a wire slightly out of the bundle that comes into the back of the cluster...

stephenc03 · #3 10-23-2008, 02:59 PM

I mentioned in my other post that when i put ground to the metal backing of the cluster the guages work fine....i am not sure about that anymore because when i have ground to it and turn on the high beams the guages still go haywire.

SD Blue · #4 10-23-2008, 10:39 PM

When you pull the instrument cluster, there are several terminal ends screwed to the chassis behind it. Also, check the engine-to-chassis ground strap located near the starter.

stephenc03 · #5 10-24-2008, 09:06 PM

Quote:

Originally Posted by SD Blue

When you pull the instrument cluster, there are several terminal ends screwed to the chassis behind it. Also, check the engine-to-chassis ground strap located near the starter.

I do not see any terminals or anything that would be able to ground the dash cluster except for the little clips that attach to the dash that hold in the cluster but even then they only touch the plastic.

SD Blue · #6 10-24-2008, 10:10 PM

Quote:

Originally Posted by stephenc03

I do not see any terminals or anything that would be able to ground the dash cluster except for the little clips that attach to the dash that hold in the cluster but even then they only touch the plastic.

Some of the electrical wires that run to the various connectors on the instrument cluster are attached to the grounding points. There isn't a "ground strap" if that is what you are thinking of.

compress ignite · #7 10-25-2008, 03:08 AM

Mercedes Engineers are fixated on using Brown insulating for Ground wires.
I'd be willing to bet,that you can find a "Ground Point" behind the IC.

stephenc03 · #8 10-25-2008, 03:26 AM

Quote:

Originally Posted by SD Blue

Some of the electrical wires that run to the various connectors on the instrument cluster are attached to the grounding points. There isn't a "ground strap" if that is what you are thinking of.

the only wires that attach to the cluster is a wire harness, sppedometer wires, clock and lights. I do not see how the cluster as a whole can get ground because the dash is insulated bu foam or plastic. Keep in mind that all of the guages worked before i took the cluster out, replaced the turn indicator light and put it back in.There is nothing in the dash or on the instrument cluster that would indicate it is recieving ground or any other type of electricity from terminals inside the dash. I own two SD and neither posess what you speak of. Are we talking about the same thing?

JimmyL · #9 10-25-2008, 10:23 AM

The ground will come through one of the wires to the plug you plug in. Add an extra ground wire with a connect/disconnect in the middle of it. You can attach it at a grounding point behind the cluster and to one of the screws that contact the metal plating on the back of the cluster itself.

stephenc03 · #10 10-25-2008, 11:47 AM

Quote:

Originally Posted by JimmyL

The ground will come through one of the wires to the plug you plug in. Add an extra ground wire with a connect/disconnect in the middle of it. You can attach it at a grounding point behind the cluster and to one of the screws that contact the metal plating on the back of the cluster itself.

I would do this but my O.C.D. gets the better of me sometimes and I feel that although your suggestion would work I would be treating the "symptom not the disease." I would like to find the source of this problem. Even if i did give ground as you suggest...when I turn on my hi beams the guages go haywire even with extra ground to them. thanks for the input

lutzTD · #11 10-25-2008, 11:52 AM

Quote:

Originally Posted by stephenc03

I would do this but my O.C.D. gets the better of me sometimes and I feel that although your suggestion would work I would be treating the "symptom not the disease." I would like to find the source of this problem. thanks for the input

mine also has an extra ground run from the rear of the dash to a screw on the cluster, you cant have too much ground. the designers had the luxery of new wire and good contacts at every juncture, you now have a 25 year old car, some adjustments need to be made unless you want to replace the entire harness and redo all of the connections. just make it with a faston in the middle so it is easy to unplug when servicing the cluster

SD Blue · #12 10-26-2008, 10:56 PM

I don't know how I can explain this any better........

Each one of the connectors attached to the instrument cluster has a brown wire. One end is the connector the other end of the wire is where it attaches to ground. If you will pull the cluster and look! There are several of these brown wires attached, with screws, to a chassis rib behind the cluster. Those are instrument cluster grounds.

So far you have not mentioned checking the engine-to-chassis ground or the battery-to-chassis ground. Since these are engine guages, the engine-chassis ground can be part of this problem. Check the ground of the headlights also.

I'm sorry but I feel like I'm repeating myself.