In the first picture, see the bar just behind the speedometer face plat with a hole at the end. Now in picture two, see the two bottom screws holding the speedometer in. The screw on the left goes through the speedometer cover, the metal bar, and the tach housing. That is where the tach gets it's ground. The ground wire from the speedometer goes to the ground point behind the instrument panel. The other end of the metal bar in picture one also supplies the same ground to the gauges on the other end of the instrument panel.

I see you are doing the odometer gears. I just did that today. Not a bad job if you get the correct gears. I didn't but it was my fault. I ask for gears for a 1984 126 but the speedometer is from a 1990 126. They must be a little different. I just had to file a small collar off of one of the gears and every thing worked fine.

Another little tip. The plastic light guides (one visible in picture 1) don't do a very good job of reflection of the dash lights. I cleaned mine real good and painted them a bright silver. I did mine many years ago and they are still bright silver and I have to turn the brightness down.

PaulM

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84 500 SEL (307,xxx miles)