wtf, went to put in a radio.... NO HARNESS!

i went to put a radio in my car, and there is no harness, no loose wires, nothing. all i found was the antenna wire... wtf?
whats a good switched 12v lead i can use to wire my radio to? everything else i know how to do, but the main power source i cant figure out, i want it to kick on with the 'accessory' setting, so i can listen to it with the car running, or not, but i dont know which wire that is.