Confusing switch wiring... Need to repurpose the switch to power/control new light strip
The wirenut you first described is the always-hot being distributed around. 

Switch 1 and the Cable 3, which is /3 cable it's involved with, go to the fan/light.  Right now, the fan/light operates off the single switch and black wire. The red wire is in the wall, reserved  for the happy day when you get a better fan that allows separate switch control for both fan and light. 

Cable 2 is a very familiar scenario. 

You know that some houses have floor lamps controlled by a switch.  The idea is you plug in whatever light you want, and this is cheaper to build also. Also, some of those receptacles are "split" - the top one is always-powered, and the bottom one is switched by the light switch.  The receptacle can be "split" by breaking off a brass tab on the "hot" side.  Then you hookup separate wires to top and bottom, e.g. Black and red. 

Well, the last guy didn't know about the tab.  He replaced a receptacle, and just hooked it up like he found it.  Forgetting to remove the tab had the effect of shorting the red and black wire.  So you can restore the switch's functionality by finding the bung receptacle and breaking off the tab.  

Or, you can cap off the red wire and use the switch for something else.