Well. Resistor has been replaced but that still didn’t help. While I had things appart I decided to check the output voltage from pin 3 with the amp installed and the engine idling. It’s outputting about 400-500mv and goes up as I rev the engine. So that’s a good sign but I am not sure if those ranges are correct.

I guess the next thing is to pull the instrument cluster and see if the tach is even connected


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Current:
16 E400 4Matic
91 300E 4Matic - 2nd car
83 300D
Past:
06 E350 4Matic
87 190E 2.6 - 1st car