On some vehicles, tying into the door triggers is as simple as connecting to the wire of the dome lamp that changes from (+) 12 VDC to ground, or vice-versa on Fords, when any door is opened. However, some vehicles have a dome lamp delay and/or an auto off feature. On many of these, you will want to locate the trigger wire(s) that will show either ground or (+) 12VDC when each door is opened, that is not affected by the dome lamp being on or off.