I thought I resolved this issue, but I did not. Originally the gauges didn't function at all (left side only) so I replaced the circuit board unit as a whole and it had power once again. I only cycled the key on to verify this, but after having the engine on I see that the fuel indicator light will come on, the fuel needle does not move from the R even on a full tank, and the oil pressure gauge pegs at 3 bar with the key on. Oil pressure sensor is fine and all wiring tests were performed to verify per the FSM. Also, fuel sending unit wiring and tests were within proper spec as per the FSM. What could be wrong? It seems like one of the wires are mixed up or something. I removed the cluster face and noted that the fuel needle which doesn't appear to move is actually being pegged down in the other direction (down) and the oil needle pegs to 3 bar independent of the running engine and actual pressure. Any help would be appreciated.

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1990 190E 3.0L

When you had the cluster out did you happen to clean the ground connection on the firewall? Sure sounds like a ground problem.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Cluster is still out....actually the entire dash is out. I pulled every connector that is under the dash going to the fuse block, all are fine. All ground connections behind cluster are also fine....but I did discover one problem. I had a faulty rear window switch on the center console which caused the instrument cluster lights not to function properly. I also pulled the wires on the front of the fuse block (terminal 15, 30, 30) and found that there is some resistance between ground and the terminal 15 connection. With negative battery disconnected and the clamp on the ground strap I get a reading when I probe terminal 15. the reading is rather high, more than 200kΩ.

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1990 190E 3.0L