2002 Yukon XL Won't Shift into 4HI or HLO

My 2002 Yukon is stuck in 2HI and the cab switch just blinks when I try to
switch into 4Hi, 4Lo, or Auto. I don't get the clunk. I've already replaced the
front actuator as well as the switch in the cab. I am getting 12V to the
actuator although I can't say for sure that it's engaging. The 4WD fuse also
tested fine.

I have now turned my attention to the transfer case motor. I am getting 5
volts to the green and brown/white going to the motor and the ground seems
to be find as well. I tried to backprobe the brown/white wire so I could test for
a voltage difference when I switch into 4Hi or 4Lo. What happens however is
that my backprobe reads 5 Volt when the connector is unplugged from the
motor but when I attached the wiring harness to the motor and test voltage
(grounding to the battery) I can zero. I have no idea what this means, might
there be a short in the motor?

I appreciate any insights!!