Something tells me the confusion is due to the different alternators used over the years by the factory and aftermarket on GM engines. Every style connected to the wiring differently.
1) The alternator that uses a "DA" plug. Its a 3 wire alternator. "BATT" terminal went to ammeter or directly to Battery Positive. The large wire on the "DA" plug is tied to the "BATT" lug. The smaller wire on the "DA" plug goes to a switched hot on the ign switch. (Factory)
2) Some GM alternators used an external regulator, ala late '60s Pontiacs. These usually have two or three threaded lugs on the back of the unit. One would say "Field" and one would say "ARM" like an old generator. Some have a "BATT" output also. These systems usually had the "BATT" idiot light on the dash, run by the external regulator. Not seen very often anymore, and they won't work right without the external regulator. (Factory)
3) One wire alternator. Basically similar to the "DA" plug model, except the DA plug is not connected. "BATT" lug is connected to battery positive. I believe that this version cannot be used with an ammeter in series with the "BATT" terminal. Must use a voltmeter to monitor system performance. Will not charge until RPM goes above idle the first time. (Not sure, think aftermarket)
4) Aftermarket "racing" alternators. Light weight, high output, low HP drag. No voltage regulation, racing/street rod use only. AC output is fed to an external "bridge rectifier" and resultant DC is fed to battery. (Aftermarket/speedshop stuff)
5) I've seen an alternator used on medium sized tractors. It has a "BATT" terminal and a 1/4" faston blade terminal below it. The 1/4" terminal is energized when the key is on to "excite" the alternator. The "BATT" terminal is connected to the battery. If power is left on the 1/4" terminal all the time, it will drain the battery when the tractor is off. (Factory outdoor power equip)
Most GM guys run the "DA" plug alternator cuz they are dirt cheap and you can get 'em at any parts place.
Hope this helps
Chiphead
