Faria instruments are inexpensive and easy to install. As Silvertip says, you adjust the settings on the back of the tach according to the stator setup. I recently switched from a V4 Johnson to a V6 Merc yet my tach setting didn't require changing; the pole count must be the same in both engines. Your control box will have a short cord with a plug for connection to an instrument wiring harness. You'll need to contact a Merc dealer to get that harness as they are specific to your engine. Then it's a simple three wire connection to the tach, one for signal, one for power from the ignition switch, one for ground. If you wish, you can add a fourth wire to power instrument lighting.
