well, sometimes it does, sometimes it doesn't any diagnose? Could be some loose wires? if you lightly tap on the dash it sometimes comes on...but i want it to work all the time, i live for the revs

 

look at the trailing coil. the coil may be bad or the harness connections loose or corroded.

Good luck

Joe B

 

when I first got my car, I had this same prob. When I replaced my alternater, it started working. Now that Im having problems with my starter, it stopped working again. Test bat. alt. and starter. And all that is inbetween.

 

Trailing coils give you your tach signal..
But the most common problem I have run across was already mentioned by live4boost..
A weak/slow starter can cause the tach not to run (actually it will cause the trailing coils not to fire at all)

Does your car turn over slowly? Check your battery and your alternator.. if you find that they are both good, but your start is still slow, change your starter..

Upon turning over your motor, the ECU checks engine crank speed.. Your car can still fire up, but because crank speed was low, the ecu thinks the car didn't start.. it then cuts the trailing coil completely, thus killing your tach signal..
Watch your tach when you start up the car.. when it initially fires up does the tach move for a few seconds, then just drops to 0? if that's the case then 99% of the time it's your starter..

 

My tach used to work intermittently like you said yours did. It got progressively worse for a while. No starting problems or anything though. The problem was a bad ground to the trailing coil.