Car is a 1989 300E

Problems:
Combination switch not working properly: High beam flasher not working, sometimes high beams turn on when using turn signal.

Cluster: Fuel gauge pegs to empty when brakes are pressed or lights are turned on, turn signal stops working when brakes are pressed, tach , clock and oil pressure gauge work sporadically.

So far I have replaced the combo switch and so those problems have been solved but the problem with the cluster remain. The oil pressure sender and ovp have been replaced in the recent past. My next step is to check the ground connection behind the cluster and any other ground points for this stuff – is there anything else I should obviously check? Tried searching but didn’t come up with much.

One more question. My replacement combo switch had that single wire coming out of the connector like in the picture but the one I removed did not – does anyone know what’s that for and what does it connect to?

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