The tach needs +12 volts with the key in the RUN position. It also needs a solid ground and the send signal needs to be receiving a signal from the engine. A voltmeter or test light can check for voltage. an ohm meter can check the ground connection. With the engine running, any voltage (ac) on the send line indicates the tach is getting a signal. I'm betting either +12 volts or ground is bad.
Thanks, I do have 12v at guage but no signal from send wire. Not sure about rectifier. but I don't seem to be getting any voltage to my battery either as I checked battery before I started engine , then after and there was no change in it. How about the stator? Does this 1988 Mercury 150hp XR4 have a voltage regulator?
