TACH NOT WORKING

Hi, I just bought a ´84 GPz550 with a bunch of things to be done, among them the tach that isn´t working. Being used to me KZ550 which has a mechanical unit, I don´t know how to fix this one, the electrical type. How can I check the connections, where does it "collect the info" from, etc.

Please help me with this one guys...

It should have a black wire that goes to the negative side of one of the ignition coils. That's where it gets the firing signal from the engine.

Thanks man, I will check it. I discovered that the voltmeter function works, so the clock is working which is a good thing...

Cheers