I will be installing an RPM gauge "tach" on my boat soon and was wondering if anyone had any advice. I don't have any experience with these or even an idea on how to hook it up really.  My motor is an 08' Yamaha 90 Fourstroke.  

Most tachs are quite simple to install. The instruction sheet that comes with it should be very easy to follow. 4 wires. Possitive, negative, lead to your lights for the light in the tach, and one lead that goes to the possitive terminal on your ignition coil. Thats the usual installation.     Happy fishing.

~B.A.S.S.~N.A.F.C.~BoatU.S.~

There are different type tach with different type input signals so you have to be careful which tach you get.

What kind of motor?  Most newer motors have a tach signal lead you connect to and the tach will have a switch on the back that you set for the number of poles tha stator runs.  Older motors may not have the tach signal lead provided.

For those type you will need a tach that picks up it's own signal.

Some of those will just wrap a wire around one of the plug wires.  

Your motor has a plug-in harness for the tach. Get a Yamaha tach and you won't be cutting wires and trying to figure things out.