I have another post about going to 16 Volt battery and it looks like a great idea. I see these 1 wire advertised alternators but when I look closer at them there is another plug area for another two wires What is that for ?? Most likely a dumb question but I dont want to buy the wrong alternator and have to figure out another plug . Thanks , What type . Brand are most guys using ??

Absent any pictures, I'd guess it's a GM alternator and what you are seeing is the regulator. There are prongs on it that are not needed or used on a one wire alternator. Some sellers / manufacturers put a rubber plug in the hole that covers the prongs so they can't be seen.

thank you

my GM delco-remy 1 wire from napa had a rubber plug over 2 prong hole

Old Delcotron. I used one for years. A little big, a little heavy, but it works. Kept the batteries up. Doesn't cost hundreds of dollars, And what I like about it, the thing is easy to work on in the field. I carried parts for it and had to fix it at the track one or twice.

Self exciting regulator makes it a one wire. Most companies plug the hole so the two wire plug can't be used.

Thanks Guys , I figured as much but was a little confused when I saw that plug spot.

Ya don't worry about that plug. I know that can be confusing as I was confused as well but it is not used.

which begs the question, why are the two wires there, but plugged ?
can this alternator be used with an external regulator using these wires ?

No. Do not plug anything in there. Self exciting internal regulator. Typically, start the engine, the alternator will not work until you bring the RPM up to ~2000. Then it turns on and charges.

NHRA would do tech and check the master switch by having you start the engine and then turning off the switch to verify everything stops. Those of us who had the alternators wired into the system had to be careful not to rev the engine and turn the alternator on. Then they got wise to that and made you bring the engine up to 3000 before turning off the master. So we had to fix the wiring.

understood about not plugging anything into those two wires, but if the serve NO purpose, WHY are they there ?
if serving NO purpose, look at how much money could be saved in the manufacture of these things. 1/2 of a penny adds up fast when you are talking millions of units installed and replaced when necessary.
there is obviously a reason [to me anyway] the bean counters allowed that connection to stay. i'm just curious as to why ?

Standard regulator...





One wire regulator kit kit with the cover....





I don't know the answer. I expect the difference is a simple change in the circuit board.

Maybe it's cheaper to use what they produce and modify it than make a large change.

I think I've seen them without the spades. Most have them.

interesting sir. Thank You !
i have never had one apart. i have just went to the Nippondenso 95 and 120 amp alternators.
Thanks again for the explanation.
the spiders in my old noggin fight to keep out other brand info, while making the cobwebs tough enough i can't remember Ma's info i have stuffed into there my entire life.