I didn't find the light switch, but I did get an ending.
Spoiler:I don't remember the first few choices, but it's easy to find the point where you can touch the wall - touch other wall - touch yet another wall - smell room - "that doesn't make sense" - kill self metaphysically - call for help - placidly masturbate - develop photos - pray - and then the choice between the next four possible options is a no brainer. 
