Open circuit switch would need what, 100,000 volts to jump the open contacts path? The fault has to be between the load side of the switch and the load. A faulty switch itself is included in this scenario. If there are additional wires connected between the load side of the switch and the load (lamp) then alternate paths come into play. A negative manifolded into several paths either works or it doesn't regarding the switch. Permutation possibilities of alternate current paths resolves troubleshooting in a hurry.