the 4x4 works but the lights on the switch do not stay soled they just blink, the vacume for the 4x4 is not getting negative , the front differnetal does not activate untule i hack the vacume manualy to lock. not sure what it could be, 99 blazer 6.0 4x4. i checked the fuses there fine, changes the computer, its not getting neggative currnet