Bloody Seat failed an MOT at half past nine today. No rear fogs; fuse blowing as soon as they were switched.
Checked the bulbs, checked the wiring, checked the fuse box, checked the switch... and it turns out that it was the front fogs, through which the switch passes on its way to rear fogs, had a short to ground and was blowing the fuse before the rears ever got turned on.
Meh.
On a *sensible* car, the switch drives relays, and individual circuits have separate fuses, but VAG decided it would be a really good idea to have *all* the running, dips, mains, and fogs going through the same switch as live, full current circuits. Genius.
The fronts can wait; I just snipped the wire to them and the rears got better. Just got it mostly back together and back round to the MOT place before they closed at one... twenty minutes to spare. Now I just have to put it all back together properly...