On the W124 wagon the motor is behind the driver side trunk panel where the spare wheel resides. Using a 17mm socket and ratchet you can open the roof by turning counter clock wise on the motor.

Often a roof that has not been opened in a while will need assistance at the rear of the metal panel, carefully pushing down so the rear of the metal panel can lower and slide backwards.

If you do have to open the roof, I'd advise cleaning the sunroof drain tubes as soon as you can.

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David Hendy
'97 Renntech E60RS
'97 GMC 2500 Sub' Diesel
'95 E300D
'88 300TE
'88 250TD
'84 L/Rover 109