1999 Toyota 4Runner Owners Manual - Page 110

4RUNNER ( ) Rear differential lock system To shift from "L4L" to "H4L", stop the vehicle and put the transmission in "N". With your foot holding down the brake pedal, move the front drive control lever. CAUTION Do not use the rear differential lock in the conditions other than above. Large steering effort and careful cornering control will be required. NOTICE Do not drive on a dry paved surface in "H4L" or "L4L" mode. This may damage the locking mechanism and the drive system. The rear differential lock system is provided for use only when wheel spinning occurs in a ditch or on a slippery or ragged surface. This differential lock system is effective in case one of the rear wheels is spinning. Before using the rear differential lock system, first shift the front drive control into "L4" to see if it works. If this has no effect, additionally use the rear differential lock system. 110