Ok, tell me how the hell this is. My old alternator had a bad bearing so I was gonna replace it. The old alternator just had the main wire with the nut on it attached and Im guessing what is a regulator multi plug was unplugged. It charged fine, never had any issues. I put in the new one and the thing wont charge. Both alternators are identical. The new one wont charge so I see that a plug isnt plugged in. I find a plug on the wiring harness pulled to the side and ziptied off, plug it in and it begins to charge and run fine... how in the hell did the old one work fine and the new one needs it? Me and my dad both, both good mechanics are stumped and cant figure this out. issue solved but id like to know how so I can better fix issuies in the future.

 

i can only think of one reason....and that has to do with the voltage regulator

maybe your old alt had internal regulator.....so hence the plug was left off.

now u might have replaced it with an alt that requires an external regulator....and hence need that plug. follow that plug lead....it should lead you to a metal box against the fender.

just an educated guess of mine. I have just done an upgrade the other way around. My old alt had an external regulator, my new alt has internal regulator. so i removed some wires/plugs that wasn't needed and took out the external regulator as well

 

It sounds like a good guess craigw1, but it doesn'tmake sense, because I know that at the very least, the 81-85 alts have internal regulators. That's why I can swap in an FD alt with minimal problems.

The connector you speak of serves two functions

1. one of the wires lets the car know that your alt is indeed doing its job. On a regular FB if you start it with the connector connected, but no belt around the alt (bad idea for long periods, but you can try it) all your dummy lights will light up. Don't ask me how I know that one.

2. The other wire supplies voltage to the regulator, but on earlier alts it's a switched source, and on s6 (89-91 FC) and later models it needs a constant 12v positive or it drains your battery.

Still no explanation for how your other alt worked, I'm just gonna guess that the design of the regulator was different and when it didn't see anything it just went into full charge mode all the time, while this one just didn't charge at all without it.

Another explanation is that maybe the previous alt was rebuilt and the person who rebuilt it just hooked the 12v source of the large terminal to the voltage regulator connector internally. That would give it constant 12v, which should allow it to charge.

Jon

Jon

 

yeah good point....maybe he linked it direct to the large terminal...but wasn't visible.

i know about the dumy lights....once i had my first gen valet parked. I dunno what the guy did, but when i got the car back and drove home all the lights came on ! when i lifted up the hood both my belts were off ! (I have the dual pulley on alt)