Truck does not go into 4-wheel high

Truck transfer case does not shift into 4-wheel high. Replaced encoder motor assembly did not help. Checked t-case shifted it manually it went into 4-wheel high no problem. Push mode selector button to 4-high encoder motor will shift t-case past 4-high into 2-high. Lights on mode selector switch come on when key is turned on then go off, then no light on to tell what mode you are in. When push any mode button 4-high and 4-low lights come on and stay on. Hope you can help. Truck listed above is a Silverado.