Truck won't start.

check engine/frame/block grounds..

Unhook the fog lights, wiring should not be hot. Disconnect and put a test light on the small wire on the solenoid and turn the key to crank position, the test light should turn on, if it don't then you have a bad ignition switch. After you get the starting fixed, then you can rewire the fog lights.

I decided to leave it until morning but I had to run an errand so I went to start it by using the solenoid and now nothing happens except a short purring/whirring noise? When I touch the solenoid there aren't even sparks anymore.

Take the battery out and recharge it overnight, most likely the short is draining the battery.

OK now for my super dumb question. I was looking at the wiring harness for the fog lights and while even I can tell whoever did it wasn't an expert I can't tell where to unhook them at. Is there something I should look for? I just see a lot of electrical tape and I notice that, what I'm guessing is the positive cable(thick and red), is disconnected.

If they did it right it would wired into the power center and installed with a relay, and used a open feed from the center. But if a novice installed it, it's anybody's guess how they did it. Trace down the wires from the lights to the power source is about the only way to find.