The fuse F10 or F16 located in the battery junction box BJB under the hood feed dash power point 1 and 2. See owner's manual in Fuses section for under hood fuse box and its fuse layout.
The DTC code P0106 could indicate a damaged MAP sensor, so it would seem logical to start with that one sensor first. If it is bad, it could cause the P06A7 vref faults. See attached file for descriptions of both codes. It could also indicate bad or shorted wiring to that sensor.
Assuming that you bought it used and the battery condition is unknown, put a charger on the battery (connect the negative lead of the charger on a body bolt, not the negative battery terminal). Charge the battery overnight or longer. See if the ASS then works. The battery has to be in good...
Is it a warning light or the passenger on/off air bag light below the radio? If a warning light in the dash, use a code reader such as Forscan to get the DTC codes.
Here is the wiring diagram for the 4x4 Switch Module. You won't see a voltage change on the switch module output as it is communications (HS2 CANBUS), not switched voltage.
My educated guess would be 0 volts, 2.5 volts, 5 volts DC in the 3 shift positions of the transfer case. I can't confirm though. But, you should see different voltages when the T-Case is shifted between 2WD, 4WD, and Neutral.
Here is the wiring to Vref and Sigrtn wiring from the PCM to the transfer case position feedback sensor. You could ring this wiring out to make sure of no open circuit or shorts to ground or to each other. I believe that it would be ground and 5 volts DC. I'll try and verify.
Here is the wiring diagram for the transfer case. You should be getting 12 or higher to the transfer case motor when commanded to shift. Check fuse F66 in the battery junction box (BJB).