Our '98 ML320 runs fine, but when we turn it off lately there has been a component that fails to shut off. Pics are attached of the part that keeps making a loud humming noise/vibration, which is under the hood on the driver's side below the windshield wiper fluid reservoir. It will drain the battery, unless we unplug the battery cable after parking. It doesn't ALWAYS happen every time we drive, but it is very noticeable when it doesn't automatically shut off. We think it may be connected somehow to the ac/heater fan control unit. There seems to be a short and our blower isn't moving any air when we turn on the fan control. Can you please tell me what this part is? Thank you for your feedback

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That's the ABS unit , the relay that runs the pump is probably sticks or the ABS controller is failing.

Thank you, SL320! The ABS light has been on for 2 years now.

There has also been some sort of electrical short, is it possible they are related?

I'd need to see a wiring diagram to determine where the ABS motor relay is. Sometimes MB places a bunch of relays in one module / box so there might be some connection but that is a guess until research is done.

I'm going to have someone check the ABS relay tomorrow.

Is there a wiring diagram for the ABS relay?

I hope this link from benzworld works. You should be able to pull the ABS relay from the fuse panel stopping the motor from running on. You may just have to replace the relay, but it may be as serious as a short or a loose
ground. In any case DO NOT DRIVE with this relay removed, I don't know if it poses a safety risk or not.