My tachometer doesn't work. I've replaced the amplifier twice. Both times it worked for a while then died. I've replaced the tachometer itself with no luck. I'm now wondering if its the wiring. I've even done the trick where you put a plastic peanut under the amp cover to force the pins down. No luck.

My questions are these:

How often does the wiring go bad?
How is the crank position read? I assume its induced somehow.
Other than the amp, is there another likely problem?
Any other suggestions that I may not have thought about?

You might have a dirty sending thing, it's not a unit, follow the lead from the bottom of the amp, down near the flywheel. Clean if neccessary, I used brake cleaner, put in a new amp, works. Also the lead you followed to the flywheel may need replacing. The receiving pins from the amp may have fallen and not making contact, I would check that first. Good luck. "Have fun in your garage" '82 300D, '83 300SD, '84 300CD