Tach problem help requested on 86 Carrera

[jet528e]

Hi All,
I know this has been discussed before, however I'm looking for a bit of advice-

Car: 86 3.2 Carrera Coupe

Issue: Tach will be reading perfect, then suddenly drop to zero. Stay there for a while then jump right back and work perfectly. This comes and goes. It will work fine for 30 min. or 2 hrs., then drop to zero for 2-3 min. then jump back and read perfect again. It has been doing this for about 2 years now and is driving me crazy. (It does not fly around erratically, either perfect or zero.)

I crawled under the car to check the ground strap on the tranny and it does seem secure and realatively clean (I had the tranny out a year ago so I assumed the wrench cleaned the connections but maybe not). I did notice a spot on the strap that seemed to be wearing a bit, but everything appeared solid.

I R/R the alternator/voltage reg about 3 months ago and it is working perfectly.

What should I do next?

I understand the tach receives it's juice from the DME (?). Are there connections I should check/clean? Should I check the connection at the Tach itself. Should I remove the Tach and send it to be repaired? Should I remove the tach, use a volt meter while driving to see if I'm getting a constent volt feed?

I spoke with one wrench to said it was probably the Tach itself, but why would that be the case if it works perfect 80% of the time.

Does anyone have a check process or series of checks to go through prior to sending the Tach off for evaluation/repair?

Thanks much for any and all help!

[catuck]

Pull the tach out and check the connections on the back. You should also check the connections at the DME under the drivers seat.