All of the answers you seek are here
But besides that, You need to locate a switched accessory source, usually at the ignition harness. You will need a meter to test the wire appropriately, and the accessory wire is active while in the "ACC" and "ON" positions (not all cars will have a dedicated "acc" position), but NOT active in the "OFF" and "Start" positions. If it is a can bus system, there may be an appropriate module/harness that will work as well. But never tap into a 5-6 volt line as that might be a data line, and may cause your car to fail to operate amongst other things.