what if some creep happens to be standing in the dark, and you want to reach in the safe without him seeing the light come on?
As far as wiring a switch in it's a piece of cake. First cut the wires so they are hanging out of the front of the box at 6". Put a pigtail in the box if it's metal it's the easiest way to do it right. Then take the 2 ground wires, and a 1' piece of ground wire and wire nut all 4 together. Then stuff those ground wires in the back of the box. Route the longer ground wire so it is out the front of the box, and cut off until about 6 inches is only sticking out. Then wire nut both white wires together. Stuff those in the back of the box too. Then take the ground wire, and attach it to the switch. Take 1 black wire, and attach to 1 screw on the switch, and attach the other black wire to the other screw. Wrap the switch with electrical tape to be safe, and screw in to the box. Put on a cover and you are done. Ask an electrician to show you next time on a job, so you get a good visual, then look back at this to remind you what you saw.
Whatever you do, don't run lamp cord. It's junk. Why don't you go to Home Depot, and tell them what you want to do, and they can set you up with the stuff you need. If it was me, I would put a box on the outside with a disposal cord whip spliced in the box to MC, then thru the wall with the MC, up to a switch box, then more MC, up to a metal light box, then a flourescent light mounted to the box. If you do use stranded wire like MC, then you need to wrap your screws a little different. Leave about 10" of black wire, and the long ground wire. Go back about 3-4" from the end of the wire, and then take your strippers, and make like you are stripping the wire. Pull the end wire like you are trying to strip that much off the wire, but don't pull the insulation off. What you want is a gap in the insulation about 1" long. Take the gap area, and wrap that around your screw, then tape. Make sure no small strands are hanging out the hollow end of the insulation. Hope this helps