The red/black will act as your permanent power/memory wire for your HU if you're using an aftermarket stereo. You can bypass the dimmer switch (they sometimes go glitchy and have dead spots in them)

Hooley flying shitballs, what is going on in that first pic in your recent post? The wiring in your truck is going to take some perseverance to straighten out. Why would anyone need to do this to a factory loom unless they added a heap of accessories (and even then you would be better off making a stand alone accessory loom and run it from the back of a fuse block...) I have a feeling there were dead shorts in the truck and whoever did this thought it was easier to hatchet the wires rather than hunt down the faults and rectify them. You're gonna need to break out the multi meter and be prepared to spend some quality time wrecking your back under the dash. It looks like the wiring is intact, just re-routed for some bizarre reason