How to add multiple horns to a single locomotive in TS?

Hello, a while back I was watching a video on how to add multiple horns to a single unit, which is used by different railroads within the sim. For example, a CN Dash 9 and a NS Dash 9 would have different horn sounds when loaded in the sim. As mentioned, I saw a video on how to do this, but have since misplaced the link, but would like to try the mod. Does anyone have a tutorial to what I am talking about?