KZ400 Probs, need advice

So Ive had this kz400 for 3 years now, put about 3000 miles on it, been a great bike to ride around but I could never get it to charge. I had an extra parts bike, I put that stator on it to see if it would charge and it did...for about 2 mins and then stopped. Im almost positive the regulator is good. I have an extra. So where should I begin? Ive checked all the wires and the fuse, all good. I wish parts were easier to get. Its a 1975, 15k on it. Any advice greatly appreciated.

What does the battery voltage read, engine off, then running @4K RPM?
If under 12v, then check the Stator ACv at the yellow wires coming up to the R/R.