Which wire is the horn wire?
 

As some of you may know, my brother got a 1997 cummins recently, and someone mounted a different horn on the driver side front fender under the hood, and it looks stupid. I found the factory one on the driver side behind the bumper. It has some wires by it dangling. One black wire with the insulation stripped on the end and one plug hanging down with one green wire and one black wire going into it. Which one is for the horn?

the horns have a 2 wire plug from the factory. drivers side