I agree with the all the troubleshooting steps mentioned above by other owners.

For my case, it was my orig alternator bearings. replaced mine with Genuine RFMD BMW (by valeo) 140amp alternator (retail at ~$600+ no tax, I got for only ~$400 including tax ) and kept the old one for autopsy/fun experiments.

Some will recommend buy RMFD or new OEM alternator for even less money. Keep in your orig alternator specs 120amp or 140amp or xxxx amp, air cooled versus water cooled .

Some will recommend DIY or go to an automotive alternator rebuild shop - defective replaceable parts like the bearings, VR and etc - most economical way to get you back on the road...

Just adding my .2 cents:


- Alternator isn't charging the battery (most cases -> the alternator is intermittently failing)
* Check terminal connections / ground cables
* Check voltage while car is OFF - should be approximately 12 volts
* Check voltage while car is idling - should be approximately 14 volts
* Check voltage at battery terminals while car is revved up a little (maybe 3k-4k RPMs) - should still be approximately 14 volts.
* Turn on everything Radio, AC/Heater and etc - the works :)

- Broken or lose accessory belt
* Check belt tension and position
* Check idler pulley and tensioner pulley

- Faulty ignition switch (can cause flickering or solid red battery light)

I never have any intentions to ignore input or defend something just because. I have no problem admitting when I am wrong. And, in this case, I am wrong about how the system works. I do stand by the poor man's methods of troubleshooting.

I agree that we are more knowledgable about some aspects of a vehicle than others and certainly there are differences in how things work from one brand to another so it is never a good idea to universally apply how things work. In my case I was thinking only of an E53 because that is forum.

JFOJ, Regardless of certification, experience or day job, I think when one declares themselves an expert they begin to be less effective. I suggest you use your knowledge to respectfully explain how something works when someone disagrees without sarcasm. I can't compare this forum to others but I do know OPs get help here. The forum was doing fine before I joined and it will do fine when I am no longer a member--none of us are an exception.

Well accoring to the "expert", he back up what I said.

Since the electrical system runs off the alternator how does the battery become a filter for spikes? And if the DME/ECU and other modules protect from spikes why is it such a bad thing to run the engine with only the alternator output if necessary for a short period of time? Rather than reference most vehicles I think we need to stick to what is true of a E53.

I said that the car ran off both the battery and alternator not one or the other. As more electrical load is placed on the system, the regulator compares the voltage that the battery is putting out along with the voltage the alternator is putting out. It adjust the alternator voltage so the battery is always being charged.

What we are failing to take into consideration is not just the voltage but the amps draw when Terminator lost power to his X. He was running at night with all the lights on and if it was in the dead of winter he might have had the blower motor on for the heater and imaybe the rear window defroster.

I have driven a car with a bad alternator on a battery as long as any non essential electrical device were left off including the radio. When the alternator to my PORSCHE crap out on me, I brought a new battery but only drove during the daylight hours. I was able to make the 40 miles trip back home on just the battery.

I understand the alternator regulator adjusts the output to keep the battery changed and provide for electrical systems draw. That seems contrary to the battery is only used to start the engine and supply current to those things that the circuit is completed when the key is turned on. And, that once the engine starts the alternator is the source of current for all electrical systems.

Update
 

Called AAA today driver came out, I said I want it towed home.
Driver said let me jump it its probably your alternator but if it starts you'll be able to make it home, I said I just want it towed. He said drive it around the corner if it workstill it'll be fine you'll make it.


So I left. Speedo abs hill decent all started going haywire.
Car started braking when driving at 50 MPH and dash all went out speedo dropped then I lost power to car and pulled over.

Tow truck ca.e towed it rest of the way home. I'll do test tomarow. It started to rain and has been a long day .

You begin your post with Never in all caps and bold type and then you say it can be done without issues. Then you say it has ruined more electrical components than anything else in history followed by that is an assumption. Confusing again.