You don't say when you want the power: always on, on when ignition is on, on when engine is running.
Always on, may drain the battery so be sure that is what you want.
Then you need to buy a test light. Most chain auto parts store will have one for around $10.
Then get one of these
http://www.radioshack.com/product.as...Fid=270%2D1204
And then find a circuit of the right size and tap into the fuse box. Using the test light, you can find a fuse that has power. If you want hot all the time, turn the ignition off. If you want hot when ignition, turn the key on and find a fuse that is hot. Add the tap to supply power to you device.
//2000CAYukon