It goes thru a factory breach, the wire is all by itself, no other wires go thru there. to be more precise. it goes thru firewall close to brake booster, about 1 inch away from top bolt that holds booster on. between that bolt and wiring thingy where your harness starts. Also I noticed there is another wire going thru firewall directly below this mystery wire, that wire goes to a 30 amp breaker on firewall and from there goes to horn relay.