Chargin system not working?

[Nsquared97]

Ok so I am working on getting my car back on the road (replaced non-running M20 with a good one.) Over the course of getting things together the battery died on me, so I jump started the car and it ran fine for a couple minutes then died, no power at all, battery light on. Swapped out the alternator for another one, and I got the same result. Took both alternators and had them tested by a local parts shop, both are working.

So this leaves me wondering what to check next. I wouldn't be surprised if the battery is no good (it's fairly old.) But once the car is running, it should run off the alternator just fine until I shut the car off, correct? The other thing I am wondering, can the alternator test good if the voltage regulator isn't working? Is there any way to test the voltage regulator itself?

Car is an '87 325is. Thanks in advance for any help/suggestions, this car has been a 14 month project for me, and this is the last thing (until something else pops up...) standing between me and driving it for the first time.

[Dissembler]

Does

A: the battery light come on when you turn the key to "on"?
B: The battery light go away when the engine fires?

The battery light is wired in series with the alternator's field coils, so if it doesn't come on and then go out the alternator won't charge. Most likely suspect is corrosion/loose connection at your C101 connector, a bad field coil connection on the alternator itself (+) or you forgot the little ground wire for the field coil (from the alternator case to the mounting bracket)

[Nsquared97]

Don't honestly remember what exactly the light was doing, I will check that next time I am up working on the car. I know I have heard of the C101, but what/where is it again? And lastly, I haven't seen any sort of ground wire between the alternator case and the mounting bracket, this may be the issue! Checking the Bentley though, it mentions this for 4cyl. cars, but doesn't say anything about a ground wire for the M20?

Thanks a bunch for the help!

[funbuddy]

This is happen when alternator is not working. But of the alternator is working then the battery is not charging. So its better if you check the charger of it.

[Nsquared97]

Had my battery tested and was told it was bad. Replaced it, and now when I turn the car to 'on' the battery light comes on, but when I start the car it dims considerably, but doesn't quite turn off. What would this indicate? Took a video to show what it looks like:

http://www.youtube.com/watch?v=5a09CO12szQ

Still wondering about that wire, is the M20 supposed to have one? If so, where does it connect to on the alternator?

The last thing I am finding pretty odd is the sunroof and other interior items like the blower work fine when the car is off but the key in 'on,' however do not do anything when the car is running. Any ideas on this? Thanks

[bmwm42]

its a ground problem most likely that thing needs a ground wire if im not mistaken plenty of threads about this shit if im not mistaken

[CabrioPunk]

Whatever came of this? I am having charging issues.