Tachometer jumpy after rheostat jumper
 

I finally got around to jumpering my rheostat. All dash lights now work. Now my tach bottoms out to zero when I let off the accelerator. When I push the accelerator, the tachometer works as it should.

When I bought the car the tach did not work at all. I put a cigarette butt in the tach amp which fixed. It does jump around on rainy days for some reason but for the most part it was working great 98% of the time.

I rechecked all connections also.

I do have a tach amp from a 1982 300SD. Will it work in my 300D/

How are the grounding connections?

The grounds on the steering column all look good.

If the SD's tach amp look the same, it should work in the 300D if it's good.