1997 Chevy S-10 tach hook up

Can you give me the manufacturer of the tach? You will need to splice the ignition control module. There should be a 12V feed to the primary coil and then another wire will feed the coil packs (secondary coils). Between the primary and secondary coils you need to check for 12V. Use a hair pin and stab that line. Connect your tach lead to that pin and then ground the tach with the other end as stated (make sure it says it should be grounded to chasis). Just try it in the engine bay so you can make sure it works before you start splicing and installing.

Its a Autometer 5inch tach with shiftlight.

Did you try the proceedure as I stated before? You might want to look at this wiring diagram and compare it to a wiring schematic of the ignition system in your vehicle. You might need this tach adapter to make the device function properly.