This is my first post. I know this is long winded but please bear with me. I bought a 2002 MCS with ~52,000 miles on the clock last month. After two weeks the alternator died. Typical, lights, loss of power steering, etc... I pulled the alternator and took it to a local friend with an alternator / starter repair shop and he said the rotor, diodes, brushes were good but the rectifier was blown. From looking at it he said someone had worked on it before but it had an OEM Denso regulator. After he did some research he said to get a new regulator from MINI since they were the only ones that he knew would work with the power steering pump. I paid $180, he put it together and it worked great for ~4 days. Then the same scenario. I pulled it out again he checked and same diagnosis. He put in an aftermarket regulator that he had and I put it together and after a week the same thing again.
He said he thinks something in the car is causing the problem but I have no idea where to start troubleshooting that since it works fine with the new regulators for a while. I asked if he can make the alternator self-exciting and Denso makes a self-exciting regulator but if I do that I know I'll need to trick the power steering pump by feeding it a 5V or 12V signal off the ignition. One wire at the alternator feeds the power steering pump to turn it on, one is ignition power and the third lead aparently feeds a signal back to the ECM but the car runs fine with a bad regulator if the battery is charged less the power steering.
Has anyone had an alternator issue like this or has anyone tried to by-pass the alternator regulator outputs? What kind of signal does the PS motor need to turn on?
Again, sorry for the long post. I hope I can find some guidance.

 

I've found a little information this morning on my quest; The power steering pump has a 3-pin connector (x6975) that controls the pump motor. I haven't pulled my pump to verify this yet but apparently this is the pin-out;

Pin 1 - 12V ignition power
Pin 2 - Alternator signal
Pin 3 - Not connected to anything

I can jump 12V ignition power to Pin 2 but it may take the pump 15-20 seconds to come up to full pressure unless you delay that signal for ~5 seconds so I may just wire it to come right on with the ignition and if the pump takes too long to come up to full pressure I can add a delay relay to hold the signal for 5 seconds and more closely match the Denso regulator output.

I'm still lost on the alternator feedback to the ECM. If it's only purpose is to trigger the dummy light then I can fix that pretty easy.

 

I doubt anyone cares but just a note to let you know what I found out. Our Denso voltage regulators are still patented by BMW so they cost $170. Once the patent runs out they will be ~$20 like most of the other regulators. From what my starter / alternator freind says, none of the aftermarket rebuilders can make a duplicate regulator that will work properly with our power-steering circuit and the OEM regualtor costs as much as the rebuilt alternator so when you go to NAPA, AutoZone, etc... you are getting an alternator with an aftermarket regulator that won't work well (if at all) or a used (but tested) OEM Denso unit that was rebuilt for brushes, bearing or rectifier issues. None of that helps me becuase I burned up two OEM regulators in short order and can't find a place or method to troubleshoot the cause.
My Denso self-exciting regulator will be in this afternoon and I'll get it installed and see what happens. i pulled the PS pump out over the weekend to investigate the wiring and see what is needed to make it run off the ignition. While I had it out I stripped it down and cleaned everything really well and found that without the alternator installed the power steering pump will actually run when the ignition is switched on but it takes ~15 seconds to come up to speed. We'll see how it actually performs later this week. I know the alternator will vary the PS pump speed from 80% to 100% so I don't know what speed I'll be stuck with. The voltage regulator sends out a ground to trigger the idiot light on the dash so without the alternator harness plugged in you don't get a dash light.
One neat feature I am going to lose is the dynamic voltage control. The ECM doesn't just feed 12V to the alternator feilds. It sends out a square sine wave that it controls to vary the alternator output. My buddy says our ECM can modify the alternator output something like 20 times per second. If you apply more than ~90% throttle the alternator stops charging to save HP. I found tha most cars do this and it actually will save you up to 3% on your fuel consumption on smaller cars. I won't have that control anymore. Once the alternator recognizes the engine has started it will charge and hold the voltage and at 14.3 volts. My unknows for later this week are what else will or won't work. I don't know if the ECM will miss the alternator feedback and stop other things like the air conditioner from operating. Electrical problems suck becuase I can't troubleshoot this with a Fluke meter and the cost to have a shop troubleshoot an intermittent short / spike or whatever is eating regulators will quickly cost more than the car is worth. It is especially difficult becuase you can't get to the alternator to read inputs / outputs while it's running. The nice thing is I'm not modifying the factory wiring so if I choose to troubleshoot or try another OEM alternator down the road I can plug the harness back in and be back to normal.
On the bright side, it now only takes me 45 minutes from the time I park in the garage until I have the alternator in hand.