Bought a used and operating 580K, but none of the gauges work. So going to do some wiring/testing. The Tach is run from the alternator, but I cannot tell if this installed alternator is the correct one. Is it possible that the unused terminal tab (below left of the black regulator (?)) is the one to be used for the Tach? Any way to test that ? If not the correct one any ideas on what I'm missing and where to look? Thanks,
Put a multimeter on it when it's running. If it's AC (6-24v?), then it's for the tach. If it reads a DC voltage then I don't think so. The tach connection is just hooked to one phase before the rectifier on all the alternators I've seen, no Case's among them though.
From just a quick look at the books, it appears the 580K used 2 different alternators. The alternator after serial number JJG0020000 is the same part number as the 580SK. Attached is a picture from my SK for your reference. Keep in mind that while most alternators provide some AC signal output to drive an tachometer, they are NOT necessarily the same. Specifically, the AC signal will be a different frequency (pulses per revolution) based on the alternator design. Additionally the frequency is dependent on pulley size. Therefore, while you can potentially replace an alternator with one from the local auto store and the batteries will charge, the tachometer may not be accurate. If you want to test you need to find the AC output pin on the alternator as Delmer stated. The frequency output will vary with RPM. Typically this will be in the 0-1000 hz range. Reference my picture, it looks like you are missing a wire connecting to your alternator. I would start by locating that in your wiring harness.
fpgm04, thanks for the post and picture. You give me great comfort. I agree that there appears to be a missing wire on mine. What I'm hoping is that that wire left of the regulator on your picture is the one for the tach. Since it matches the location on mine. It appears that previous owners to this hoe removed much of the wiring, and likely the tach wire is one of them. When I get back to the hoe location, I'll run a test wire from the tab in the pic to the tach terminal (I know which one from the wiring diagram in the service manual) and hope that it works.