From this thread:
'84 W123, no tach amp?
Quote:
Originally Posted by Rick76
Your car is a Federal or Canadian version. You have a speed sensor on the rear of the engine that has brown and white wires going to a 2 pin connector C155. It is located to the left of the brake booster (right if looking from front). You can unplug it and check the sensor coil resistance. Also check to ground for infinite resistance.
From C155, wires go to C154 on the back of the cluster. Wire colours are now brown/white (pin 1) and white (pin 2). Pin 3 is the power feed to the tach that comes from fuse 12 (8 amp) and is black/red.
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This quote makes me think that I should be able to connect the two wires coming out of the sensor directly to the 2 of the pins on the tach, and then provide 12v to the tach on the 3rd pin.
Has anyone ever tried this specific setup/hack, i.e. wiring sensor directly to tach? Or rather, does anyone know which of the sensor wires should go to the which of the pins on the tach?