Instrument Panel Lights Grounding Question

[mainmech]

I am attempting to install a universal auxiliary switch panel into my 2015 GMC Sierra 2500HD.  The switches are equipped with an "always on" backlight as well as a pilot light that comes on when the switch is in the activated position.  The backlights dim with dimmer control like the other instrument panel lights.  The pilot lights can be wired optionally.  They can be dimmed like the other lights or be wired for 100% brightness.

But first, to make any of this work properly, you need to know whether your vehicle's instrument panel lights are grounded straight to the chassis ground or has a varying potential supplied by the dimmer control.  I can't find a wiring schematic that includes the instrument panel light dimmer system.

Has anyone come across this problem or know where I can find the schematic I am looking for?