Window will not go up - yet motor and mechanism are fine

This one has me puzzled...

My passenger side window will go down, but not go up. And the motor seems completely fine.

Took the mechanism with motor out from the door.

If I reverse the polarity, the motor will rotate in the upwards direction, and not downwards. If I attach the wires directly to the car battery, it rotates fine in either direction, depending on the polarity.
Measuring the voltage of the wires going to the motor shows nothing suspicious: plus or minus 12V, depending on whether I press the window up or down switch...

What on earth could this be??

Have you tried the switch from the other side or if you have the switch off try it on the drivers side to see if you have the same fault!

I betting that the switch has shitty contacts

Will try switching the switches. Thanks for the quick suggestion!

So, was it just the switch ?

It was indeed just the switch... thanks again Cobber & TaffD.

Obviously I do feel a bit silly for not having started by swapping the switches first, the absolute easiest thing to do.

Hopefully I can just clean the contacts of this switch and get it working properly again. Cobber helpfully described that process here

Glad to hear you have identified the issue. Hope cleaning up the contacts works.

I managed to clean the contacts - switch works great again!

There was a lot of blackish dirt in there. I used a small flathead screwdriver and some tissue with isopropanol alcohol.

Reinstalled the mechanism and door trim, and window works again. Time for a beer and a spin (in no particular order)!

Thats a great result.