my alternator stopped working this weekend, leading to dead battery and long wait for a tow truck, now that its daylight i noticed the small blue wire on the back of the alt was disintegrated at the connector, what is this wire for? is it a + source, or a ground of some sort? would anyone have a copy of the wiring diagram for the 78 320i? the bmw320i.com website is expired, thanks
Cabe

which blue wire? which small wire? take a pic and then make another connection for it. maybe it connects the diodes together for grounding or something, i don't remember my class on aviation electrical and how that stuff works

sorry I didnt have any pics. On the back of the alternator there is a 10ga brown wire with a ring eyelet bolted to the alt, and just below the shield for the eyelet is a smaller (16ga?) wire that plugs into the alt with a spade connector. From what I read this wire operates the battery light in the cluster. I hooked it back up and charge light works now, but stays on all the time. I gave the car a boost got it started and was running for about 45mins, after all that, the battery voltage with the car running was still only 11.5V. I guess now I need to take the alt off and see whats with it, my question now is, is there an external or internal voltage regulator?

i think its internal but i'm not 100 percent sure on these cars as i have very little time working on them. i'm just going off the other cars i have worked on and that i have seen no external regulator in the engine bay on mine.

I couldnt find one in there either. Thanks!

I'm not 100% sure about the pre-80 cars, but my 83 has an internal regulator. Cost $13 at BavAuto.com.

Yeah, I just checked: Part Number 30 062 , $12.95.

K thanks for that. Is there any way I can test the regulator in the car? Or have I got to pull the Alt and take it somewhere to have it load tested? Does anyone have a copy of the wiring diagram for the charge circuit?

The regulator is internal. The brown wire is a ground, like all brown wires on a BMW. The blue is the 'exciter' wire. Power is applied to it when the key is on, and it activates the alternator in a way. I won't work without it. Then of course there's the big red wire where the power goes to the car.

So the exciter was the one I replaced, do you know if there is a way to do a full field test (bypass the VR), or needs to be taken into a shop with a tester?

If you jump it and it runs then the wire is connected. However if it doesnt charge or start then you have a bad alternator, battery, or connection.

yup, check it the old fashiond way. start it up and disconnect the battery. if it dies, the alt is bad. if it stays running then the alternator is good

Oh I had already established the alt was bad since the car started fine and didnt start to die until I was driving, the battery is only a few months old. I was just trying to determine whether or not it was the winding or the regulator, a full field test I had done today tells me its the regulator, i may end up putting the higher amp one from a e30 318 in though, from what ive read its only a matter of sourcing the lower bracket with the adjuster. Thanks for all your help.