Don's pretty knowledgeable, but I've got a Puch that I'd like to put some signals on as well. Where are you getting the rear rack?
As far as wiring goes, you can use a toggle switch as long as it's single pole, double throw (SPDT). You can get various brackets to mount the switch onto the handle bars then. If they're not mounted there and you have to take your hand off the bar to operate them, I'm not sure what the point is, you could just give a hand signal.
Get a wiring diagram for your ped, and find a hot wire from the wiring block (if you've got one), or you could simply tap into the headlight or taillight and pull from it's power. Make sure you know what voltage your magneto is so you can get the right bulbs. It makes sense that the lowest wattage bulb that has decent visibility is the one to get.
If you wanted to go battery powered, I've heard that you can hook a gel-cell of the same voltage as your magneto to the magneto, then run add-ons from the battery. While the ped is running full power, it's charging the battery. But even a regular battery that you have to change wouldn't be bad. For the amount of power and use you'll need just to run signals, a battery would probably last all summer, and if you brought it inside for the winter may even last more than that.
Let me know if you need more help. The worst thing here is routing the wiring from the back to the front. Be sure to try to run the wire next to the wiring that's already there for the tail light, you know this is a safe path free from moving parts.