I have a 1992 formula with 305 TPI. Tach does not work at all, but if I plug in a Snap-On scan tool to the ALDL port, RPM reads fine. Could the tach itself be bad?

Any connection I could check? THanks for any input.

 

If you search around there are a lot of posts on how to fix speedos that don't read correctly... you should be able to get all the info you need from ones of these posts.

 

Speedo works perfectly. Tach is the gauge that does not work. Can the tach go bad on these gauge panels and all the rest of the functions are fine?

What actually feeds the tach? I figured if the computer is seeing the correct RPM (as the ALDL indicates) then I should be able to find the source of the RPM signal going to the dash and work out the problem from there.

 

The Tach reads off the negative terminal on the distributor.

 

I have an Accel 300+ (plug and play) hooked up. Does this effect the tach signal?

 

I'm not sure, but if it is an aftermarket ignition box the tach signal should run off the negative on the box.