99 Yukon Denali 4x4 problems

Hello, I have a 1999 Yukon denali (http://www.2carpros.com/forum/viewtopic.php?p=112735#) 5.7 Engine with 95,000 miles. Recently my 4wd stopped working and I have the service 4wd message. First I replaced the 4x4 Actuator on the front axle, still nothing, Replaced the switch on the dash nothing happening, then i replaced the encoder motor and plunger according to a bulletin by gm. Everything seemed fine i'm able to switch between gears but the service 4wd light is still on. Now today i'm driving back out of a spot and boom no lights on the 4wd selector on the dash. checked the fuses all worked and getting power can hear clicking on comming from the fuse panel. When i first power up the vehicle i notice the light light up but don't stay on please help are they any more switchs the control this 4wd it's becomming a nightmare.
Thank in advance.