I have been having issues with my passenger headlight flickering on my 04 Blazer. I was installing a new battery tray when I noticed three ground connections below the tray. They were screwed into the front metal just below the tray and above the 4WD vacuum actuator. The “grounds” were extremely corroded and rusted. (One was a 10-12awg or so wire, so it was carrying a decent load). I cleaned them with a wire brush and crimped on new wire connectors. I finished by coating them with dielectric grease. No more flickering. I have no idea if these ground wires are correlated to the lights but it solved my problem as electricity can be a fickle issue. I hope it helps others. By the way, if you remove the battery tray, the bolts are secured by 2 “crimp on” square style nuts which may fall down never to be seen again in the crevices of the frame.

I was wondering and feel better now so thanks for letting me know.