When a problem develops, many folks pop the hood of their Trailblazers/Envoys for the first time and notice this red wire that isn’t hooked up to anything. It comes unhooked from the factory and has a specific use.
That stud on the fuse box which is for that red wire is a convenient place to get power for low current accessories and it’s got its own dedicated fuse! That stud is constant power, not switched. It’s not a place to hook jumper cables up to.