there should be a sensor already on that motor. should look like about a 1 1/4 round black plastic disk with the top either a light blue color or white. 3 wires?  can't remember. on the passenger side?  the wires are probably already run in the main harness to your console and hooked up to the motor. from what i remember ( been a long time) , all V6 motors have everything in the eng harness to the console from the factory. the cutoff was probably under 90 hp when it might have been an option in the harness.  look at another boat with that same motor if you can and check what color wires come from the trim switch to where they are connected, if not straight to the trim switch. and yours should be the same.