Hey everyone, have a bit of a strange electrical problem. I have an 03 MCS JCW. Bought it with a blown motor and rebuilt it. Replaced the original alternator during the rebuild now It runs but doesn't charge. Replaced the alternator again and same thing. Have also used 3 different batteries. Had both alternators bench tested at autozone and checked out okay. Not sure what those voltages should be. Have continuity from the body the the alternator frame, and from the alternator post to the battery cable.
I think I've narrowed it down last night. I tested the alternator field in the car by putting something metallic near the pulley and turning the key on. No magnetism. Then I took the alternator apart and put 12v across the field terminals, bypassing the voltage regulator, and got magnetism. So assuming the voltage regulator on both alternators wasn't bad, I'm thinking one of the 3 wires in the harness plug is supposed to be grounded at some point to excite the field. Right now on those wires I get 9.5, 11.5 and 10.5v. not sure what normal is supposed to be on those wires. So I guess a few questions:

Would someone be willing to perform the first test here on their R53?
Should I have voltage on all 3 wires after just turning the key on? Does anyone have an idea what the voltage on the 3 wires from the wiring harness (ECM, F39 fuse and battery light I believe) are supposed to be?
Does anyone have a wiring diagram that shows the interconnection between the power steering pump and alternator? Is it through the battery light or the F39 fuse? Having trouble finding one that shows it all
Am I way off here? lol

TIA!

Edit: Found this thread that might be relevant.

 

I'm just throwing this out there. I just replaced my engine and recall two heavy guage power wires intersecting/connected at the starter... Not the power steering pump. I have no idea if this helps. Do you have the big service manual. If not, I have a copy I can try to see if there is a useful wiring diagram a can take a shot of.

 

Provide your email address and I'll send you the R53 wiring diagrams from my Bentley manual.

 

Ever have any luck solving this? I just bought an 05 R53 with similar issues. Alt is good, battery is good, grounds are good, fuses and relays good. No charge.

 

Was cruising along one day and abs light pops on . Next all warnig lights come on then guages go out . Next power steering stops. Turned her off and wait three hours and she starts right up . Drive 3 blocks battery dies car stalls,I have no power on the small wires at my alternator . All fuses are good . I even sent the dme out for checking and its good , The car just stopped charging one day . Wierd and now the power steering pump runs as soon as the key is switched on . Put a new alternator did nothing. Changed power steering pump did noting . Car runs fine until the battery dies . 2006 R53 .If anyone can help im at my wits end.