Motorcycle Repair: 1983 Yamaha 920 virago tachometer works intermittently, yamaha virago 920, electronic tach

Question
This bike has no cable for the tach just electric wires from the sensor to the electronic tach itself.  It is like the car tach you connect to a spark plug wire but it is permanently wired from engine sensor to tach with wires in a wiring harness.  I checked the wires and found nothing wrong.  I do not know how to test the sender unit or the tach itself.  Any advice?  Once again it is not cable driven!
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Followup To

Question -
The tach on my 1983 Yamaha Virago 920 works sometimes but is not steady  or always correct, sometimes it does not work at all.  I checked all the connections at the tach and followed the wires to the point they go into the engine and found nothing wrong.  Should I get a replacement tack (used ones still available on internet) or is there a sending unit that may be the problem?  Any help appreciated as I am about to give up at this point.

Answer -
There has 2 b some kind of "drive" for the guage.  It can't tell RPM by wires.  I would say that u have a bad tach cable, but it may b the tach itself.  Remove cable and make sure it turns freely.  If it does, then I would replace the tach and the cable as well.

Answer
Ah, u r the one who wrote those nice comments about me.  Lol, u still expect me to help?  Well, I will.  U took my words and laid them out to your needs and then wrote me down.  What I meant was for u to find the sensor, gears, or whatever the hell the wires r connected 2 and see if it's all in good order, shape, funtionabilty.  I understand it's not "cable driven" guess I was just 2 wordy.  The sensor must b replaced, or at least that's where I would start.  Much cheaper than a tach and without a scope u r not really gonna know if it's working.  However, there should b some kind of voltage on the sensor itself, but it may not b an entire 12 volts.  Could b around around a 10th of a volt, half a volt, a volt . something, or an entire 12 volts.  I would also OHM the sensor to make sure it has a complete circuit.  Let me know and please, no more bad comments till u have all the facts.  Have a good one and let me know!