Diagnostic Aids

WARNING: This page is about a different car, the 2017 GMC Yukon XL, 2017 GMC Yukon, 2017 Chevrolet Tahoe, and 2017 Chevrolet Suburban. However, it is still accessible from the selected car via links, so may be relevant.

Other failures on the run/crank ignition 1 voltage circuit may cause erratic behavior on the front axle control signal circuit.
The transfer case fill/drain plugs are good sources for ground.
A TRUE B+ carries enough current to light a test light.
A DIAGNOSTIC B+ is a low current circuit that DOES NOT carry.