There is a terminal marked TACH on the distributor cap. Connect one tachometer lead to this terminal and the other lead to a ground. On some tachometers, the leads must be connected to the TACH terminal and to the battery positive terminal.
1975-77 models with a six cylinder engine utilize an HEI distributor with an external coil. For these particular vehicles, connect one tachometer lead to the TACH terminal on the ignition coil and the other one to a suitable ground.