Tachometer stopped working

1995 D90 NAS - Once in a while the tach won't work on initial start but eventually came on after a few miles. This happened 3-4 times during the last year. Now it stopped completely. I cleaned the connection on the negative post on coil. The connection appears good behind the dash as well as the connection at the back of the alternator. I unplugged it at the alternator, put a meter on the alternator side and I get 3.6 volts (I think.. I have a nice klein meter, but am a poor operator of it.) I increase engine speed and the voltage appeared to increase as well, so I figured the alternator was working ok. I find it hard to believe the wire broke or the tach just failed. Or should I be getting more voltage off the alternator at that connection? Thanks