Well, two wires are for the speed sensor and one for the clutch.

Try putting the ground off your test rig to the compressor body and hitting the clutch wire (probably blue) with 12V.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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