So, you're looking for a source of 12 volt power? I know where you can find it 
If you lay down in your car, head under the dash, feet hanging out the door, you'll see approximately this:
Obviously you won't have a lot of the extra wires that I've added to my car, or that neon tube. But we're just looking at the fuse box here.
In the pic, you see two wires which I have labeled, #1 and #2. They are both sources of 12 volt power. #1 only has power when the ignition key is in the ACC or ON position. #2 always has power. Whichever one you want to use, you'll need a standard 1/4" female spade connector to access the fuse box's male spade connector, which is hiding up in each of those grey plastic squares.
If you lay down in your car, head under the dash, feet hanging out the door, you'll see approximately this:

Obviously you won't have a lot of the extra wires that I've added to my car, or that neon tube. But we're just looking at the fuse box here.
In the pic, you see two wires which I have labeled, #1 and #2. They are both sources of 12 volt power. #1 only has power when the ignition key is in the ACC or ON position. #2 always has power. Whichever one you want to use, you'll need a standard 1/4" female spade connector to access the fuse box's male spade connector, which is hiding up in each of those grey plastic squares.