New 4 W Drive Actuator On Front Axle Doesn't Work

[als_gmc_2000sierra]

I bought a new 4 wheel drive actuator for my 2000 gmc sierra and it doesn't work. I get power in the brown wire that is on the harness connecting the actuator. When I press the 4Hi on the switch on the Dashboard it just blinks, I hear the encoder motor on the T-Case when I change from 2Hi to 4Hi but the front axle never engages into 4 wheel drive. No 4W service light comes on...ever. any thoughts ...thanks in advance