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I got a problem with my 79 Bronco. I just pulled the worn out 351C out of it for a 400M that I had in a different bronco. I got it running, and noticed that the Alternator is not charging.... I tryed an alternator that I had sitting around, and nothing.... So I went to the local Auto ZOne (which was my first mistake) and boaght a rebuilt one. The alterator light would go out, once I got the engine upto 2500 RPM. Once I let off the gas, the light would come back on. So, I took it back, and got my money back. I then went to a local Farm & Fleet (big farm chain in Illinois) and picked one up there. Same thing. I tossed a new voltage regulator in it, and now it will not even charge at all! I know the battery isn't in the greatest of shape... Just to verify that it wasn't charging, I started it, and pulled the possitive battery post, and it died, so I know it is not charging at all... The alternator is a 3 wire setup. BAT, FLD, & STAT. Someone please verify for me, that the WHITE wire goes to the STAT, Orange on the FLD, & BLACK on the BAT... I DO have 12 volts on the WHITE wire(s)
i am betting that your grounds arent making good contact with the frame etc... especially since you did a motor swap those tend to be the last things to connect and the most often forgoten.
I found the problem! I found a third voltage regulator, in a box of old parts, tossed it in, and son of a gun, it started charging!! One of the regulators I was using, was new!!