New member here - first cry for help.
The green headlight indicator on my dash is on when the headlights are off. It goes off when I turn them on. EXCEPT - it also goes off if I set the parking brake, which turns on the brake indicator light on the dash. Seems kind of weird to me. But I've never had a GM truck before. Perhaps this is normal?
Completely normal. The green "headlight indicator" is actually a DRL (Daytime Running Light) indicator. These trucks use a module under the dash to illuminate the low beam headlight bulbs at a lower brightness level than normal using pulse width modulation for DRL function. When you turn the headlights on using the switch they go to full brightness, therefore DRLs are off and the dash light turns off. Same deal with the parking brake, engaging that disables DRLs.