This switch is used to enable or disable the 12 volt trigger sensing circuitry on the amplifier. If the switch is set to the ON position, the power amplifier will remain in standby mode until it detects a 12 volt signal at the 12V Trigger Input on the back panel. When the 12 volt signal disappears, the amplifier will return to standby mode. This switch should only be set to ON when 12 volt triggers are used in the system, if they are not the switch should remain off or in the Signal Sense position (where applicable).