4 Wheel Drive Actuator for all 6.5 equipped K series P/U trucks, Suburbans and Tahoes using the 2 wire actuator.

This is usually the reason why your 4 wheel drive front axle won't engauge. It is also known as the TLA Thermal Linear Actuator. When you shift the transfer case into 4x4, this actuator engauges the front axle. Its located on the front axle facing the rear of the truck. It installs in minutes. Has 2 wire harness connector.There is a switch located on the transfer case that supplies power to this actuator when in 4x4. Check and replace that switch also. Its p/n ssd-016 also in this category.