Greetings! We purchased our house a little over a year ago, and I've been updating some of the older wiring--it was built in 1912, with a back addition added in 1995. In any regard, the wiring in the detached garage was a bit strange, in that a switch in the back addition controlled all of the lights in the garage, both external and internal. There was also a switch in the garage, but it did nothing if the switch in the addition was not turned on. Not wanting to have the interior garage lights turn on when we wanted to have just the exterior (driveway flood) light on, I decided that I'd just remove the switch in the garage, and wire it so that the switch in the addition simply controlled the exterior lights, and then I'd add a new switch in the garage to control the internal lights. To that end, I opened the junction box in the garage that had two wires coming into from the house. One I assumed was the load (12-2; grey in the picture below) and one was from the switch (14-2; white in the picture below). I turned off the breaker and confirmed this to be the case using a circuit tester. I didn't really notice it at the time, but the wiring to the switch in the garage was old 3-way wiring with no ground. That said, I proceeded to wire the switch like I would when the source is at the light: black from the switch wire to common, black to black (to the light). When I flipped the breaker back on, the light was on, though the switch in the addition was off. When I flipped the switch on, the light turned off, so its reversed. I took off the wall plate to the switch in the addition, and it was a 3-way switch, with 14-3 running to it. Reminder: what's coming into the garage is 14-2 (see picture below). I haven't yet figured out where the red traveler from the house is going. Also, all of the wires in the addition switch are in the same piece of romex. The switch is wired with the common on the right of the switch on the black nut, with the red traveller on the top left, and the black traveller on the bottom left. Any idea what is going on? I don't think it matters, but for the sake of being complete, the wire in the garage that feeds the lights and outlets is 12/3, at least until it gets to a junction box on the ceiling, where it ties into the old ungrounded wiring that I am planning to replace after I figure out this mystery. I'm not sure it will help, but here's a picture of the junction box in the garage. I had already separated out the switch in the garage, so I'm not sure exactly how it all originally fit together: [url]https://goo.gl/photos/rwstYMvr5DXBiSE7A[/url]

I don't know much about electrical work, but from what I've searched so far it seems to either be a GFI or maybe a bad switch. Quite often when I turn the light on in my bathroom, it trips the GFI which stops the light from coming on until the switch is reset. My knowledge on electric work is quite low, and this will be the first time I try a hands on job myself. I've done a few google/YouTube searches and I'm confident enough I can do this, however I'd like to ask you all if there are any factors a noob like myself might overlook that could cause serious issue. I know to make sure the breakers are off, but I don't want to overlook something that might cause myself, or my home, any harm. I'm not willing to assume this is 100% simple at my experience level