Greetings,<br /><br />I purchased a 1983, 50 HP, 4 cylinder Mercury. I decided to install a tach. I purchased a Teleflex tach off E-Bay. It was new and still in the package, never opened. Went to my Mercury dealer and purchased a wiring harness that goes into the remote box. I hooked the tack up per Mercury instructions (purple to ig, gray to sending and black to ground). I set the dial switch to 6P per Teleflex instructions.<br /><br />Went to water and it showed 4000 RPMs. WOT should be 5000-5500. My prop was a 14 pitch. I decided to move to a 12 pitch in order to bring RPMs up as well as get better hole shot. Installed prop and she came out of the water but the RPMs is still at 4000 WOT. I checked the connections and re-read the instructions about the dial settings. 6P is where it should be.<br /><br />I have a Sears Engine Analyzer I use to work on my old truck and my old Mercruiser. It checks RPMs, Dwell. amps, volts, etc. Can I use it on an outboard to check to see if my new tach is bad? The way I use it on my truck is to hook the cables to the battery and a lead to the coil and one to the alternator. What else could be wrong so the tach does not go above 4000 RPMs?<br /><br />Thanks,<br /><br />Terry G.