With the trim cover removed to access the sunroof motor, you can see - I think near the centre of the motor gearcase - a large slotted head screw. You can turn this with a blade screwdriver to manually close (or open) your sunroof.

No relay - the switch handles all the current.

The switch toggles the Red and the Blue wires so that one has voltage from the Red/Grey and the other gets grounded to the Black, depending on whether you are trying to open or close the roof. This is the way it reverses the motor.

If you can manually reverse the wires and get motor operation in the "bad" direction, it suggests the Black and Grey/Red wires to the switch are OK, also the Blue(?). If, while attempting to run the motor, the Red wire shows only ~9V at the motor, you need to trace back through the wiring to see where the voltage drop is occurring. If the Red shows 9V at its switch terminal, the problem must be in the switch. If 12-13V there, check along the wiring to the motor.

IIRC, there is a connector in the wiring between the switch and the motor, probably to simplify installation at the factory. Check there.
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Bob: son's XC70, dtr's '94-940, my 81GL, 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.