Is the tachometer for a 1985 300 TD controlled by the "tachometer amplifier" that I have read about? I think it isn't, I think by 1985 there is a different way of the tach working. Can someone please tell me -- Maybe it's something I can clean or plug in or something. My tach works occasionally. I would really like it to work more often.

Thanks.

No hints from anyone?

You're right, there is no tach amp. Do a search on the ovp relay.

The tach sensor on the 1984 and 1985 vehicles is on the rear of the engine, down under the oil filter. It reads revs off the front of the flywheel/flex plate. Signal goes to a box under the dashboard where it is conditioned and used by such things as the A/C et. al. The output of the box (OVP or over-voltage protection relay) feeds a nice signal to the tach. X2 on aaa's advice - lots of data here on OVP and tach.

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1984 300TD