there is a black/yellow wire that comes out of the van wire harness, and when i put on my aftermarket harness is comes out brown. what is this wire for and what do i do with it?

there is a black/yellow wire that comes out of the van wire harness, and when i put on my aftermarket harness is comes out brown. what is this wire for and what do i do with it?
This is the wire that runs from the dimmer switch and dims the display on the factory installed stereos . Usually not used in aftermarket units . Just make sure its taped off so that it doesn't short to anything.