I don't recognize the picture of the instrument cluster in the Alldata post but it isn't an '87 300D or TD. The '87 has a three-pin connector for the tach with only two pins used.

The tach signal goes through the electronic diesel system (EDS), which is in the component compartment behind the battery. If the EDS module dies, your tach won't work. The EDS module is protected by the OVP relay so that has to work also.

Other than damaged wiring, which is more common than you might think, especially in cars with missing belly panels, the ring gear sensor and the tach itself rarely fail.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970