Well now I’ve done it.....

[Audio Einsteins]

I’d Love to say “being an installer in the aftermarket electronics world for 28 years , I don’t screw up anything anymore.” 
but ..... that’s not the case . 
I was installing a set of gauges that work wonderfully in our 2017 duramax hd and decided to test for illumination w/ control . I know better but I used a traditional Mac test light to find the output wire . (Rather than an electronic)
well guess what ...... no more low beams / tail lights and markers from the BCM ...... No!!!!!!!. High flash works and lights after ignition works but not the fore mentioned nor the chime indicating I left the lights on in manual . 
A).  Not  sure if the headlight switch is a logic control switch but my suspicion is I may have given a lan bus wire at that switch too much ground impedance and shorted it with the test light.

I feel that’s the issue as it certainly worked just fine before I tested around . Tried auto and manual and not getting 12v to the fuse box on either side. 
B). Im hopeful there is another safety link I don’t know about or can test that may get me back to driving at night, and to allow me to pull my embarrassed head out....  once again to it’s normal location on my shoulders.