Another "my tach stopped working" thread
 

Yes I did a search and no I never found my answer. Really there isn't much posted as far as a actual solution so....

My car is a 89 turbo

My tach started acting up last summer, where it seemed it needed to warm up first, usually took about 5-10 min of driving and then it would come on. I check wires and connections and cleaned the grounds but it still acted up. This winter, For no apparent reason it started working fine only maybe 1 out 10 times it would need to warm up to work. With nice weather now around I started driving more (I also have a truck that I drive when it crappy weather) and last week it stated acting up again, every time, and it would take a good 20min of driving before it came on, and now it won't work at all. I Cleaned the grounds again, swapped out coils, did all the mentioned fixes and nothing worked. I'm afraid the tach mechanics in the gauge Custer might be the culprit, here are my questions....

does any one know how to check the tach, maybe with a volt meter to see if it's working?

Has any one swapped out just the tach guts of a cluster? And if so do you have to use a certain model tach?

I have an extra cluster but it's out of a S5 NA, can I use that tach?

Does any one know of any thing else that maybe I haven't mentioned that I can do?

should be a bullet connector on each of the T and L coils.
use a jumper wire and attach a wire to the Bullet connector at the leading coil and at the trailing coil.
It may bring your tach back.

Thought the tach only worked off the trailing coil?

And yes you can use a s5 cluster, but you need to modify it slightly, there's a thread on how to make it work

Edit: my bad, i see you said a s5 N/A cluster, that i'm not sure of being as it doesn't have a boost gauge, unless you already have an aftermarket one

Both coils have a bullet connector diagnostic port. If you jumper/connect them to each other then the tach signal will be pulled off of the lead coil's bullet connector and passed to the tach gauge. The thing is why the tach stopped in the first place, which could be caused by a faulty tach, faulty trailing coil or faulty wiring and possibly a faulty ECU as well.

I will give this a try and see what happens.

The cluster is out of a s5na, but I pull out just the guts of the tach and want to put them in my turbo cluster. They are different as the n/a's red line is 8, and the turbo is 7.