I have a '16 and cant for the life of me figure out what this switch does.
It shuts off the Roll-sensing Curtain Airbags. Those airbags will go off if you roll the truck. But they might also go off while off-roaring without rolling the truck. So Toyota gave us a way to turn them off.
From pg 50 in your owners manual:
Deactivating the curtain shield airbags in a vehicle rollover
ON/OFF (hold for a few seconds)
The “RSCA OFF” indicator turns on (only when the engine switch is in IGNITION ON mode.)
The roll sensing function for the curtain shield airbags and seat belt pretensioners will turn back on automatically each time the engine switch is turned to IGNITION ON mode.
■ This switch only should be used In a situation where the inflation is not desired (such as during extreme off road driving).
■ Operating conditions when the “RSCA OFF” indicator is on
●The curtain shield airbags and seat belt pretensioners will not activate in a
vehicle rollover.
●The curtain shield airbags will activate in a severe side impact.
●The seat belt pretensioners will activate in a severe frontal collision.
WARNING
■ For normal driving
Make sure the “RSCA OFF” indicator is not turned on. If it is left on, the cur- tain shield airbag will not activate in the event of an accident, which may result in death or serious injury.