Be very careful about what you switch off.
Many years ago I was involved in a smoke incident. We smelt burning and wondered what it was. It smelt electrical. The flight engineer checked the galleys - nothing found. Then, suddenly, we were engulfed in smoke which reduced the visibility to less then six inches. We thought we were on fire. Someone suggested switching off the master radio switches - which seemed a good idea at the time, but they also switched off the horizon, the altimeter and the compass, leaving us with only the ASI, VSI and turn & slip.
We nearly lost control of the aircraft. After a while the smoke cleared and we landed back at max landing weight. Fortunately, the smoke came from the air conditioning system and was not toxic, otherwise I would not be here.
You need to react quickly - but make damned sure you know what you are switching off!