Calling Alternator Wizards: E12 Alternator Swap Question

[Guest Anonymous]

Yes, I mean E12, not E21. I have a question about swapping in an e12 alternator. I found one today in a remarkably nice '75 530i at the salvage yard today (the half hour or so it took to get the alternator out cured me of wanting an early Fiver).

Anyway, it fits fine so the physical install is a snap. I referred to Trent T's instructions for the E21 alternator but it doesn't quite seem to be the same for this one. Here's what I did: installed it, B post to red wire, it now grounds through its casing (solid mount, no bushings). The internal regulator has a three-prong plug receptacle identical to what is on the 2002 alternator. There is also an individual spade marked D+ in addition to the D+ on the regulator.

I plugged the 2002 alternator plug as-is to the alternator using the regulator spades. I disconnected the plug at the regulator on the firewall. Car started and ran well (no more idle dipping when the H4s go on, fan speed remains constant when lights go on) but I didn't have an alternator idiot light at all, even just at ignition on. If I reattach the plug to the regulator, the idiot light comes on and stays on.

What do I need to do here? I obviously don't want to hurt anything and I also want to have my charging idiot light. What's the scoop?

Thanks much folks...

Tim

'75 2002

'88 325is (fer sale)

[Guest Anonymous]

a lot of those guys are prior or even current 2002 owners, just a thought. Paul you are moving really soon, I've had a couple e-mails on the decklid but that has been it, sorry about the whole situation, I take full blame for it.

Tim.

[Guest Anonymous]

The D+ terminal is the terminal for the warning light. Are you sure your E12 alternator is internally regulated? It doesn't sound like it is to me, as every internally regulated Bosch alternator I've ever seen only had a stud terminal for connecting the main (big red) charge wire, and a D+ spade terminal for the warning light. Why not test your charging system to see if the alternator is charging with the regulator disconnected? It sounds like it is, but if it isn't, you probably need to connect the regulator. Incidentally, the light aqua blue wire in the three wire plug is the warning light wire which goes to the D+ terminal on my E21 alternator.

HTH

Colin

[Guest Anonymous]

You know, I had that thought too....the alternator has what appears to be a replaceable regulator bolted into it (and I do know what the regulator looks like). I will ask on the First Fives board and see what should be in a '75 530i. I hope I haven't bolloxed this up already with my choice of alternator.

Second question: when you refer to the aqua blue wire, does that come out of the plug that goes into the 2002 alternator or the plug that goes into the 2002 external regulator? Please break that one out for an idiot like me...all my wires appear to be black, but they might just be dirty.

Thanks again...I'm an idiot.

Tim

[Guest Anonymous]

Tim,

Your wires are probably dirty. The aqua blue wire is in the plug that went into the 2002 alternator. On my car, the E21 alternator has the big red wire bolted to the big stud terminal, and the aqua wire removed from the three-wire plug and connected to the D+ spade connector. The rest of the three-wire plug is just tucked out of the way, and the original regulator is disconnected and removed. The plug for the original regulator is just tucked out of sight.

HTH

Colin