I have a yamaha digital tach hooked to the engine. It will jump around in values while running. I also have a NMEA 2000 network attached to the engine as well as a NMEA 2000 compatible gauge and the RPM reading from that gauge reads steady numbers while the yam digital tach is jumping around. I know the tach jumping around can be a sign of a regulator/rectifer going bad. It can also be a bad electrical connection to the tach. Just wondering if the regulator/rectifer was going out, would the erratic RPM readings be reflected in the NMEA attached gauge as well. I would imagine so but I want to confirm. The digital tach is old and I can do without it but I want to make sure the regulator/rectifer is OK.
