I'd expect it should be possible to test using a signal generator with a 12V output. I plan to put a CRO across the tacho input to determine the parameters but won't be for awhile yet.
1974 Moto Morini 3 1/2 Sport
1972 Moto Guzzi V7 Sport
1975 Moto Guzzi 850-T3
1976 Moto Guzzi 750-S3 (owned since new)
1978 Moto Guzzi 850 Le Mans Series 2
1983 BMW K100
1983 BMW K100RS