To pass a light wire through a wardrobe shelf
my suggestion would be to drill a small hole where you want the wires to pass. Make sure the hole is big enough for the wires to slide through. Then use a jig saw to cut up to the drilled hole.
I'm assuming you will remove the shelf before you drill. You could try attaching a widder board to the shelf then drill through both of them so that half of the hole is through your shelf.
As Rymea suggested, put your shelf securely on top of a piece of wood that you are OK with drilling into. If you are comfortable with a drill and are able to drill down vertically with little problem, you really needn't even clamp.
Depending on the diameter hole your wires require, use the proper drill bit, hole bit, or spade bit. Mark where you want the hole (I suggest coming in just a bit from the edge to minimize the risk of the bit "running" off it's mark). Use a nail to hammer in a pilot hole for the bit to settle into.
Place your drill bit into the pilot hole and slowly begin drilling. Keep your speed slow until you are certain you're drilling straight down into the pilot hole. Continue on until you feel the bit pass through your shelf and into the wood beneath. Clean up the edges with sandpaper and paint/stain if you desire.
If your shelf is removable, can the wire go behind or on the side of your shelf? Sounds like you just need a notch in your shelf. If you need a small hole use a small drill bit...half hole is pretty hard to do.