I'm putting in a android head unit and connecting a reverse camera amongst other things. The reverse camera is straight forward, it takes power from the reverse light when illuminated which then turns the camera on to send the image to the HU. I'm thinking it would be useful to have a button which can independently operate the rear camera without having to be in reverse or lighting the reverse lights. The part I'm not sure of is what I need to add to stop the reverse lights coming on when the dash switch is operated. Can I stick a diode in somewhere? Someone else mentioned a relay but that seems a bit of a faf.