The switches are found in the door frame usually. Sometimes at the hinge end or at the lock end. Never at the top or bottom. They are usually a small black plastic botton sometimes covered with a rubber boot. There is a screw which holds it in place and when you take it out there wil be one wire attached to a contact which when you open the door provides the earth to light the bulb. 99% of the time the door switch is rusty or knackered just swap it out as they are only a couple of quid.
JB, September 2008
