You flip the first switch and wait few o minutes, then u turn off the first switch. Next you flip the second switch and open the door. If the lite is on, it means that the second switch is the right one, if the light is out you touch the bulb - when its hot, that means that the first switch is the right one ( the reason fot flipping the first switch, waiting and turning it on was to make the bulb hot), if the bulb is cold - that leaves the thirt switch to be the correct one.
Sorry if I messed up the english or didnt explain the solution properly, but it should be good enough.
COM202 Loch Ness - Europe