Re: Tach hook up on 1975 50HP
In the past, tachs from OMC and Merc were not interchangable. More recently universal tachs had a J/E connection, not used for Mercs. Today, universal tachs work for both brands. So the answer is probably not, but try it. Try a 6P setting and see if you believe the RPM reading. You should also need to connect +12VDC and Ground to the tach. These will be white and black wires, respectively. Ususally there is a three prong connector for the tach on the MerControl box.
That Merc will have a solid brown wire tach signal. Remove the wrap cowl and see if the brown wire is connected to a yellow wire on one side of the rectifier. If not, then it is likely connected to the switchbox, and must be moved to the rectifier. Consult a wiring diaghram from the maxrules website.
