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Q: Why won't my 4WD engage? on 1995 Toyota 4Runner

The drive shaft turns, and the front drive axles turn, but the dash indicator light never comes on. When in the dirt and in 4H or 4L only the back wheels spin. the front don't grab at all. Could it be or is it the lockers, cuz I'm pretty sure they're automatic, Maybe they're malfunctioning? I don't know. Please Please Please help.
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The Automatic Disconnect Differential (ADD) allows engagement and disengagement of front differential from 2WD to 4WD while vehicle is moving. On vehicles with ADD, a flange is mounted on the front hub which is splined onto axle shaft connected to side gear shaft on front differential. Locking hubs are not used with the ADD.

When transfer case is shifted into 4WD, the ADD is shifted into 4WD by operation of ADD solenoids which control vacuum supply to the ADD actuator. The ADD actuator engages clutch sleeve with intermediate shaft in front differential and side gear shaft, providing 4WD operation. When vehicle is in 4WD, the 4WD indicator light on instrument panel
will be illuminated.

NOTE: ADD solenoids may also be referred to as ADD Vacuum Switching Valve (VSV).

Operation of transfer position switch and transfer pressure switch completes ground circuit which allows ADD relay to operate. When ADD relay operates, voltage is supplied to the ADD solenoids. The ADD solenoids operate and control vacuum supply to ADD actuator for 4WD operation .here is a diagram of the location of the ADD system
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