[dylan604]

> studs are typically (US) 16" apart,

if they are not in the typical 16" and your not near a corner, try 18" and 24". I'm in a house from an infamous builder in the early days of the cookie cutter developer cutting every possible corner and then finding new ones to cut, they are definitely not on 16". In fact, I doubt there was a tape measure used at any time during the build, and most things just seem to be placed by "that looks about right" measuring system.

Electrical boxes and light switches are the only ones to have faith in. Other types of boxes (like cable or phone) could have been added after the fact and just be attached to the dry wall if there's even a box.