Russ,
Had the same problem last year with mine. One tach would work sporadically when I agitated it, then it just didn't work at all. Checked/cleaned all connections at gauge and engine, no response. Turned out to be a bad tach. Bought one used of the right type and vintage ('89 VDO) from a guy on this site. Works perfectly!!

Found out later that the movement within the tach is fairly delicate and gets frigged-up after years of service. New vintage tachs from VDO cost a bundle, like 400 bucks!!

So, find a used one. Lots of guys here have swapped out their gauges for new styles. Good luck.

Thanks guys. I'll try the above suggestions.

For four hundred bucks I'd replace all the guages with Livorsi. Want to at some point anyway. I want white faced, red needle, and black numbers.

Anybody have trouble with their fuel gauge? Mine went on the fritz towards the end of last summer. IF I remember right, it would stay towards a quarter tank with speratic bounces all over.

Knock on wood (as I knock on my head), that's okay on my boat.

I second this one. Pull the plug apart, clean the contacts and coat with dielectric grease.

Ran a "continuity" test yesterday. One of the light grey wires, the one that runs back to the dash, failed the test. Checked it to the connector, and okay to that point. So I just ran a new wire from the dash back to the coil, clipped the light grey wire and wrapped and wire tied it to the new wife to designate it's replacement, and the tach is now working perfectly. Thanks for the suggestions guys.