‘95 Merc 115 RPM guage not working

My 95 Merc 115’s RPM isn’t working and the voltage on the dash gauge is showing just shy of 12 volts while running either at idle or wide open. I have replaced the stator, voltage regulator, and trigger. I would think that it would be the the gauge, if it were not for the voltage gauge reading on the low side.
Any ideas?

check you actual voltage at the battery. My gauge runs low on my boat as well. IF your tach does not work at all, probably the gauge. I do not know if there is a way to check them, might google it.