That is definitely some strange behavior, that red/ white is power direct from battery. The voltage should only be changing on the 2 pin plug to the blower motor by the J126 module based on signals from the Climatronic control module in the dash. Sent you a page on its function. Think you will need to get a scan tool that can take a look at Hvac control module and look at measuring block & output tests.
We have had this all tested and I don’t understand what’s going on. It randomly stopped working, so I bought another used genuine blower motor with the fan module and nothing. Connected to 12v and fan started to spin, the wiring is all good upto fuse box and climate control module. Also tried different climate control module.
3 different mechanics have tried to have a look and don’t know what the problem is.
Some people have suggested some wiring on the bonnet hinge but there isn’t any wiring there on my model of car.
And also my rear demister and heated seats are still working !
Yes the SC4 fuse has been know to pop because of a wiring short at the hood hinge for the heated washer nozzles but seeing that your heated seats work fuse is good. As you know if that fuse pops it also takes out the climatronic module and a few other items.
So I take it you have swapped these and still blower did not work
What about the used blower motor resistor?? Was that also swapped?