Large switch
The large switch was a device created by the Quintessons and was located in the very depths of Cybertron during their rule over the Transformers.
The true details or capabilities of the device was not known except that it was linked to every Autobot and Decepticon to the point that, if switched off, the device would result in all the Transformers becoming inert. The switch has no known proper name, only being referred to as a "large switch" by the Quintessons.
Fiction
Generation 1 cartoon
The Quintessons used their new Decepticon allies to assault Cybertron while they secretly sent a commando team of Sharkticons to the depths of Cybertron to push the switch to the down position which would have deactivated all the Transformers. The Sharkticons failed in their task because of Blitzwing and Rodimus Prime, however, the mad Galvatron thought that the switch was related to the Decepticon Matrix of Leadership, which was a Quintesson lie, and activated the device. This stopped the Transformers war and would have left Cybertron back into the hands of the Quintessons.
That is, until Spike Witwicky used Rodimus's gun to destroy the Switch which reactivated the Transformers again, and they were really ticked off at the Quintessons.... FFo5