How do you install a tachometer in 1996 Hyundai accent?

There are 3 (maybe4) wires on your tachometer. One +, one - and one gives the signal to the rpm. You must connect this third wire to the ECM (ECU) rpm outlet (White wire) or directly to the ignition coils negative wire (blue - yellow)

If there is a fourth wire on the rpm, that is the backlight. Connect it to the dashboards backlight system.

Good luck.