Replaced the alternator on my '73 with a rebuilt Delco 3 wire unit from the local parts store. Car started and ran fine after the replacement. About 2 months went by as I worked on the cooling and brake systems and the battery went dead (new battery). Figured it was just the idle time that got the battery, so charged it up and took it in to have it load tested just to be sure Battery tested fine. Ran a parasitic drain test on the system to see what I had and it showed 360 milliamps. From what I can gather it should be closer to 100 ma. Since the only thing I had changed recently was the alternator, I checked the amp draw as I disconnected the blue and white wires going to the #1 and 2 positions on the alternator internal regulator. Figuring that with the key off there should be no amp draw on either of these terminals, I disconnected #2 wire and there was no change in the 360 milliamp draw. When I disconnected the #1 blue wire, the amp draw went to zero. Figuring this was indicating a bad diode in the alternator I returned it for another alternator and installed it. Doing the same test, the parasitic draw was now 260 milliamps and also went to zero when I disconnected the #1 blue wire. My question is - is this 'normal'? Just seems to me that with the key off, this terminal should see no current. If I'm wrong here - what am I not understanding about this circuit? I'm not an electrical expert, but know you folks are out there. Would appreciate some guidance as the next step is obviously to just pull fuses and hope I find the drain. Thanks

 

I will write this:

When I do parasitic drain tests to find what is causing a power drain. When I find the problem...and more than likely it is on in teh alternator. I still have the alternator connected and I get '0' on my tool.

SO...I think you still have a problem in it.

DUB

 

The wires to the alternator are likely swapped. You should not have any power on the terminal #1 wire when the key is off. The wire for the #1 terminal should only get power when the key is turned to the running position.

 

Thanks Dub - just as I thought. I'll keep looking.

 

Thanks - I'll try swapping the #1 and #2 wires and see if this changes the readings. I hooked up these wires the same way that my old alternator was wired, but that may have been wrong from the get go. My research does indicate that GM convention is that the blue wire is hooked up to #1, which is what I have done, but worth a try to see if they are crossed up.

 

I swapped the #1 and 2 wires and got "zero" amps on the meter!! Hope it's this simple. Thanks for your guidance - much appreciated..

 

The cheap replacement parts makers can't be bothered to make sure they get it right. Replacement connectors pigtails have the colors wrong and some replacement alternators even have the terminals swapped.

 

Thanks Lionel - - I'm finding that parts are not 'correct parts' seemingly all to often. Thanks again for your help. Really saved me a lot of aggravation.