If you have an FJ equipped with a rear locker the A-Trac system can be activated simply be installing a factory A-Trac switch.  Evidently most FJs are factory wired for the A-Trac system even if the option was not included on the original build.  The switch can be obtained from many sources for approximately $50.

tech

What is A-Trac?

The Toyota Active Traction system is computer controlled traction control available on various Toyota vehicles.  The system senses differences in wheel speed and automatically transfers torque to a wheel with more traction by applying a certain amount of braking force to the slipping wheel.

A-Trac in action...front wheel is off the ground and has no traction.  The a-trac system applies braking force the slipping wheel transferring torque to the wheel with more traction.

Using a small screwdriver or similar flat surface pry out the blank hole cover to the right of the factory RR DIFF LOCK button.

The factory wiring is attached to the rear of the blank.  Detach the plug from the blank.

Next you must follow this procedure to activate the light.

With the engine running and the rear diff not engaged...

Push the A-TRAC button
Shift into 4-Lo
 

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