You did not say which model. The K5 and K4 have pads near the bottom. The pad above the USB jack is ground and the other one is "switched" battery voltage. You can turn the power on and off in diags. It also gets turned off in screensaver mode after a timeout.
On the K3, the top slot in the left side is power, and the bottom pins in the bottom slot in the left side turn ON the power to the top when they are connected together, and also serve as a power ground return path. The official K3 lighted cover does that, and there is an LED hack in the K3 Index and Hardware Index wikis (linked to the Master Index sticky thread in this forum).
When you post yours, please add it to all the Index wikis that it applies to (Hardware, and Kindle models). Thanks.
P.S. On the K4 and K5, you can connect to the accessory power pads with wires attached to small magnets, such as those you can "borrow" from the ends of a plastic rod from you kid's "Magnetix" toys: http://www.magnetixgalore.com/magnetix/ You cannot sell a magnetic power connector unless you pay royalties to Apple, who patented using magnets in a power connector. Apparently you can patent simple obvious ways to use magnets now. Some people even patented using white plastic on USB connectors. You can patent using colors like WHITE now? 