I'm trying to set up my van's two dome lamps so that they dim after a short delay (10 seconds or so), exactly like the ignition switch lamp delay option.

My question is this- do I need to use one delay relay per dome lamp, or can I wire it so both lamps are controlled by one delay relay? I plan to use an ignition lamp harness setup for the dome lamps, but I'm not quite sure how to properly wire it.

Black and brown wires are the only two wires running to each dome lamp, with the brown being hot power and the black being the ground wire controlled by the door jamb switches. The van uses four jamb switches if that makes a difference.