Need to find a live wire under dash of Chev class C

My 2004-based Chevy only ran the radio in the IGN position. I don't know if they have changed the factory wiring, but there was a four wire harness from the chassis, behind my radio. (The MH maker installed the radio.) The four colors were brown, red/white, black, and white. They hooked up the main radio power to the brown, which was an IGN circuit. The red/white is hot all the time. I don't recall the functioning of the black and white, but they didn't come into play for what I was working on.