One of methods of search of a point of short circuit is in getting a safety lock and to connect a control bulb or the voltmeter to plugs of connection of a safety lock when all other elements of electric equipment of this chain are switched off. In a chain there should not be tension.

Move wires here and there and watch a control bulb.

If it lights up, so somewhere in this area short-circuits one of wires, it is probable in that place where isolation was wiped.

The same test can be carried out on any other element of a chain, including the switch.