On my 123's The relay is located on the driver side fender well under a black plastic cover...should be two little ice cube relays....If they have the same number of pins you can swap them for a test....Most of the Aux fan problems are worn out brushes and shaft bearings that have gone dry....

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)