The Magic of the Horn Circuit - Route 66 Hot Rod High The Magic of the Horn Circuit. After entering the dash area, the horn wire is routed to the horn relay. The coil side of the horn relay, is routed to the steering column. I used a 1980s GM Van steering column as it didn't have a ignition key. It has a GM color coded standard connector where the black wire is the horn how to test GM mechanical horn relay chevelle a body - YouTube Mar 06, 2016how to test GM mechanical horn relay chevelle a body Chris Craft. GM delco-remy horn troubleshoot and info chevelle chevrolet DIY do it yourself Simple horn wiring for your hotrod.