Wife's 2003 R50 is the car I'm currently driving as my R50 is laid up due to an axle leak of some sort. Once I get this sorted, it's on to that. So for the last few months I have seen the battery light flicker on at times under heavy electrical load or at idle, say at a stop light. I failed to take any voltage readings when it was doing this, though. Lately, it's been flickering on more often and even was doing it while driving about 30 mph, at that point the power steering cut out. So I figured it was time to order a new alternator. Way Motor Works helped me find the right one and I ordered it.

Today was install day. Took the Valeo unit out and put in the Bosch rebuilt one. Before I buttoned the car up I strung the new belt on and started it up. To my amazement, the battery light stayed on. Measured battery voltage before starting the car was 12.11 volts. It dropped down to 11 something, went up to 14 something for a few seconds, then dropped back to 11~. I figured I had a bad rebuild but when I put the Valeo unit back in it did essentially the same thing- shows charging for a few seconds and then not, even if you rev the engine. With both alternators, it's different than before- it used to charge most of the time with occasional flickers of not charging, now it's the other way around.

Belt is new, tight and routed correctly. B+ connection on alternator is clean and tight. Two pin connector is plugged into the alternator firmly and correctly. Battery dates from 2017. Service light in tach has been coming on and off over the past few months but I haven't read the codes- it usually goes off in a day or two so I assumed it was probably an O2 sensor throwing a code. Should I check for codes and clear them? I also haven't done the "Alternator Testing Values at ECM connector", which involves measuring the Pulse Width Modulation (voltage) at idle.

Any ideas here? I suppose the the rebuild could be faulty in the same way as the original alternator, but that seems unlikely. But the alternator is connected directly to the battery, and it shows 11~ volts at idle. That says to me that the alternator just isn't working. Does the PWM/two pin connector actually control the alternator- turn it on and off like the A/C gets turned on and off- or is that two pin connector signal just there to tell the engine to idle up if the electrical load is increased?

Thanks-

Val