In addition to what is in the manual (which is included below), you can deduce that there can not be more than a 6 mph speed differential between the wheels, which is accomplished by the 3 mph limit to engage locking
With our bypasses, the actuator will be powered to engage all the time, even if there is a large speed difference between the wheels.
From "Owners" Manual:
This vehicle is equipped with electronically locking front and rear differentials. These differentials, when engaged, mechanically lock together the axle shafts forcing the wheels to spin at an equal rate. This allows the vehicle to maintain its momentum and prevents it from becoming stuck.
The locking front and rear differentials should only be engaged during low-speed, extreme off-road situations where one wheel is likely to not be in contact with the ground. It is not recommended to drive the vehicle with the differentials locked on pavement due to the reduced ability to turn and speed limitations.
CAUTION!
• Do not lock the front or rear axle on hard surfaced roads. The ability to steer the vehicle is reduced and damage to the drivetrain may occur when the axles are locked on hard surfaced roads.
• Do not try to lock the rear axle if the vehicle is stuck and the tires are spinning. You can damage drivetrain components. Lock the rear axle before attempting situations or navigating terrain, which could possibly cause the vehicle to become stuck.
The locking axles are controlled by the axle locker switch. The switch has three positions, AXLE UNLOCK, REAR LOCK, and FRONT/REAR LOCK. Under normal driving conditions, the switch should be left in the AXLE UNLOCK position. In the AXLE UNLOCK position, the front and rear axles are unlocked. In the REAR LOCK position, the rear axle is locked. In the FRONT/REAR LOCK position, the front and rear axles are locked.
NOTE: Even when the axles are in the AXLE UNLOCK position, the limited slip differential in the rear axle still provides torque biasing capability for moderate low traction environments.
During the command to lock the axle, the indicator light will flash until the axle is locked. After the lock command has been successfully executed, the light will remain on solid. To lock the rear axle, place the vehicle in 4LO. Refer to “Four Wheel Drive Operation” in “Starting and Operating” for further information. Move the axle locker switch position to REAR LOCK while traveling less than 3 mph (5 km/h). The RR indicator light will remain on when the rear axle is locked.
NOTE: Left to right wheel speed difference may be necessary to allow the axle to fully lock. If the indicator light is flashing after placing the switch in the REAR LOCK or FRONT/REAR LOCK position, drive the vehicle in a turn or on loose gravel to expedite the locking action.
WARNING!
Do not use the locked axle position for normal driving. A locked front axle is intended for off-road driving only. Locking the front axle during on-road driving will reduce the steering ability. This could cause a collision and you may be seriously injured. To lock the front axle; move the axle locker switch to FRONT/REAR LOCK while traveling less than 3 mph (5 km/h). The indicator light will be solid when the front axle is locked.
NOTE: The rear axle must be locked before the front axle will lock. To unlock the front axle; move the axle locker switch to REAR LOCK. The FRONT/REAR LOCK indicator light will go out when the axle is unlocked.
NOTE: The axle lockers could be torque locked due to side to side loads on the axle. Driving slowly while turning the steering wheel from a left hand turn to a right hand turn or driving in REVERSE for a short distance may be required to release the torque lock and unlock the axles.
To unlock the rear axle; move the axle locker switch to AXLE UNLOCK. The REAR LOCK indicator light will go out when the rear axle is unlocked.
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M.P.W.R.G.A. 
