Okay. Some of the newer threads has me a little confused. I have a 72 Cutlass. Did this car come with an external or internal Alternator? The parts stores say internal. I have the regulator on the firewall. I bought a new wiring harness from M&H. It plugs into both the external regulator on the firewall, and the internal regulated alternator. Anyways, it would not charge with that setup and the dash light was on.
So, about 1 1/2 years ago, I just put on a 1 wire and it charges fine. However the dash light is still on. I would really like it to be correct and not the 1 wire setup. Any help?

 

All 1972s came with an EXTERNAL regulator, but this was a transition year and there were external regulator alternators with the internal regulator plug configuration. If your aftermarket harness is wired correctly, the factory-style external regulator alternator should work fine. As for the one-wire alternator, the THIRD wire that was eliminated is the one that controls the GEN light on the dash. Short of converting your alternator back to a factory-style three-wire, there's no way for it to work the idiot light. As an FYI, there are a lot of reasons why NOT to use the aftermarket one-wire systems. This is one. If you want to eliminate the external regulator, you simply need to jumper the wires in that four-pin connector, as shown here:

 

Thanks Joe:
I was hoping you would answer. Looks simple enough to jumper the wires as in your description. I agree with the 1 wire setup. Not good. I'll pick up another correct alternator soon and give it a try. I do know the difference between the ext. and int. as I rebuilt them in the 70's. Thanks again.

 

Before you go out and buy another alternator check yours first alot of one wire Alternators have the internal regulator in place you just have to pull off the rubber plug cover and see the 2 conductor plug , at least that's the way mine was from Summit racing

Here is a good article on the swap and look at the picture most aftermarket one wire alternators have this plug

http://www.hotrod.com/techarticles/m...regulator.html

 

Thanks. Yes, mine does have the internal regulator in place. So I should be able to just plug in my harness and jumper the wires at the regulator and be good to go?

 

I'm not sure it's that simple. The one-wire regulators must have some sort of internal connection to the #1 terminal that allows self-exciting when the wire to the GEN light is not used. How that internal connection works or doesn't work when the light is connected is unclear. Similarly, there must be an internal connection from the #2 terminal to the BATT terminal. This internal connection will override the external sensing wire and negate that function. A better choice is to simply swap in a stock regulator THEN connect the plug.

 

You are right Joe I used an Aftermarket one wire alternator and I used a different diagram which I just posted mine works Great now I have a 100 amp Alternator and a cleaner looking firewall and the Idiot light works in the dash , one more thing the older style alternator plug won't fit the newer 10-12si Alternator so you might have to salvage one or you could pick one up at your local auto parts store for like $5 bucks .
Like Joe said if you want to keep it simple and "original" just get the proper replacement parts ...

 

Thanks for the replies. I have the external on the firewall, just unplugged right now. I think I just will eliminate the 1 wire as it is only 42 amps and go with the correct parts and a 63 amp. Thanks again

 

I used one from an 87 Cutlass that came with a 94 amp alternator. Bolted up like it belonged there. I'll probably never need that much in this car, but I like to have power in reserve if I ever need it.