This alternator has a sticker on it that says ":This alternator must be externally regulated" There is a 2 prong green plug that plugs into the alternator, as well as a red cable that bolts to the terminal. The battery is discharging when the car is running. The battery is in good shape.
if there is an external reg, you should be able to follow the wires from the alt to the reg.
Now on my fj45 wagon with a 350chevy and GM alt, when I bought it, it had an externaly regualated alt on it.........BUT there was no external regualtor.......just plain ole NOT there.......now wonder it never charged worth a damn! Replaced wtih a GM internal reg alt......all better now
Keith; I've got a '76 FJ 40 and I had the same problem with mine. I don't know very much about electrical systems but I can at least share what I went through. The 40 has an external regulator similar to the one pictured above. I took my truck to the auto parts store and had the alternator tested in the vehicle. They just hook up a pretty sophisticated looking tester to the battery terminals. In my case the readout said low diode output. The guy that tested it said that meant I needed a new alternator. Put one in, and I still had the same problem. Ditto when I replaced the regulator. Finally took it to a mechanic that knew how to trace down electrical problems, and he finally found that the wire that goes to the fuse box was disconnected. I think it's called the exciter wire. I'm not sure what the moral is other than don't throw money at a problem if you don't know the root cause. Also a lot of people will tell you that if you're draining the battery it's a bad alternator. Ain't neccessarily true as I just learned the hard way. If you think it might be the alternator, I'd take it out and have it tested.