I have a 91 RS. Tach was dead (needle stays all the way left, doesn't move), so i bought an z28 instrument cluster with 145 speedo from Hawks and installed it. Tach is still dead and I am almost 100% confident that the tach in this cluster was good. I need help with further trouble shooting.

I looked at the distributer and there are two connectors that plug into it. Its so far back there that I can't tell if either on is marked "tach," but they both look like they are on there securely. When I stand on the drivers side of the car, the connector that is farthest from me (passenger side) seems to lead back to the fire wall. I managed to get ahold of it, (not an easy feat) take it off, blow compressed air on the connector and reseat it. Tach still dead. The other connector goes to another component that looks similar to the distributor, but is smaller and slightly farther forward and toward the driver's side. It is connected to the distributor by a spark plug style wire. anybody know what this component is? More importantly, can anyone tell me for sure which one is the tach wire?

What is the next step to troubleshoot it? Thanks

 

Try measuring the network resistors in the circuit board located in the dash panel under the tach. Also search the forums for "Tachometer fix". Should be in the electronics forum.
Good Luck

 

When I did the cluster swap in my car, I had to put the PC board from my cluster into the 145 MPH cluster in order for the tach to work correctly.

I would get another 115 MPH RS cluster, pull the PC board for the tach, and put it in your 145 MPH Z28 cluster.

My guess is your original PC board went bad, and the 145 MPH Z28 tach pc board isn't the same.

 

According to hawks and everything else I see on here the 145 cluster should be a direct swap for teh 115. no modification needed.

Am I missing something here?

 

Yeah bro, I'm sure the physical tach itself is a direct fit, but if any of the resistors on the pc are not at the correct value, or no resistance at all, it's not going to read correctly. The way I fixed mine was by soldering in a "jumper" resistor on the pins not reading right to bring it up to the correct value.

 

Type in 90-92 tachometer fix in the search forums and you will find some really great info to help you.