83 300sd speedometer - PeachParts Mercedes-Benz Forum

Paulc66t · #1 08-27-2007, 10:36 AM

I have just started having some problems w/ my speedometer. It started not working and then bouncing around some. Today it seems to be working but definately not at the correct speed( reads 55-60 @ 70mph). I also noticed the gas gauge was not registering imeadiately and then coming up after several seconds. The Tach has also been flaky as well( I have already done the quick fix -shimming the amp). I think there may be grounding issue. I removed the cluster yesterday and could not find any obvious problems. All the connectors looked Ok. How or where can I check the ground to the cluster? Should I check anything else?Where does the speedo input come from? I can't find a ground strap to the motor( similar to W123 onthe bell housing). I added an addition strap from the chasis ground to the block( didn't seem to help).

Paul

Paulc66t · #2 08-27-2007, 07:47 PM

Anybody??

LUVMBDiesels · #3 08-27-2007, 08:58 PM

The ground wires are brown in color. According the the wiring diagram, there is a ground behind the instrument cluster. It should have a bunch of brown wires attached to it. This ground does a lot. It is used for the cluster, hazard switch, radio, all the cluster switches and lights, rear defogger, etc.

You probably have a bad connection from the cluster to this ground contact.

Let me know if you want me to send you the ground distribution pages from the circuit diagram.

Paulc66t · #4 08-28-2007, 08:30 AM

I can see the bunch of grounds behind the cluster. I need to find where tehy come into the cluster. It must be on one of the plugs. I assume the wire should be brown as well. I guess I can measure resistance between the plug ground and the chasis.

LUVMBDiesels · #5 08-28-2007, 08:32 AM

The ground wires in the cluster are also brown.