Tachometer terminal connections / wiring a tachometer
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
There are three terminals on the back of the tachometer: one connects to the positive terminal on the coil, one connects to the negative terminal on the coil, and one connects to ground. The back of the tach is engraved near each terminal, though the engravings can be difficult to see (especially with the tach mounted in the dash, as the mounting bracket obscures the engravings). The photo below illustrates each terminal connection.
If after you have confirmed all the wires and connections, the tachometer still doesn't work. Unhook the wires. A bad tachometer can really mess up the signal coming from the coil and make your bike run horribly.