Quicker way. Hold a piece of steel ( like a screw driver ) against the alternator pulley or back of the alternator, if it sticks the field is staying on or there is a shorted diode for the stator. Actual shorted not what some call any electrical fault.

Thanks! I'll do this today! (love these kinds of quick tests!)

Ok, charged the Battery and hooked it back up - turned the Ign Sw til the dash lights came on, then I put a small screwdriver blade against the pulley and body and there was zero magnetic attraction

Hope I don't need to start the engine, but I can probably get my hand close enough to the pulley to test it with the engine running if I need to?

Does me not seeing a magnetic attraction mean my alt has no shorted diode or a
stator?

Thanks for the help.... When I am able to, I'll disconnect the B+ wire and will try that test if needed.

LarryT
06 E350AWD

To do a parasitic draw test on this car its best to use small jumper cables and a Digital multimeter.

firstly get a starter pack or jump cables from one car to this one from the posts in the hood so you dont lose any saved settings etc.

now disconnect your battery negative and connect 3 small jumper leads to the battery and the terminal to complete the circuit. You can now remove the jumpers from the front of the car.

push in the door latches or tape the push button switches on the door pillars along with latching the trunk and hood and taping up any push buttons there too to simulate the car having all doors closed.

leave the car alone for 30 minutes to an hour.

take your DMM and select it to amps, change the leads position on top too (if your DMM requires)

remove one small jumper cable from battery post and connect it to one lead of the DMM, remove another cable from the battery terminal of the cars wiring and connect it to the DMMs other lead.

you should see some reading on the DMM proving that your circuit is complete. Now finally remove the last jumper altogether from the battery post to the terminal - this way all your amps are now flowing through the DMM, at this time your reading should be less than 50 milliamps.

if its more than this - find your fault by isolating the circuit at fault - on the W211 I start with the power seat module under the driver seat.

Best way is to measure voltage between the pins of each fuse with a new separate DMM, any live circuit will show some volts as voltage loss happens when any circuit is loading up. The voltage should start at some microreading and drop to zero. If it doesnt drop to zero. thats your fault. You can then isolate that fuse/circuit and see the DMM hooked to the battery and terminal. The problem with just disconnecting fuses on modern cars with can and lin bus is that this action can awaken/reboot some modules rendering your testing useless.

If your DMM starts to beep the autoshutoff feature (if so equipped) - then immediately plug back the 3rd jumper lead you removed from the battery post and terminal, cycle the DMM on/off to restart the autoshutdown counter in it. and remove the 3rd cable again.

tip: - buy a new generic battery terminal and attach three regular thin wires to it - 16 gauge is enough, attach three small alligator clips to the wires, these wires are now jumper wires - Now you have a handy tool that makes life/work easier.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)