This attempt at modeling the air line for the horn used 0.019" wire, which is pretty heavy stuff. It's also a best guess based on limited photos and a wrong guess at that. The air line originates from the dynamic hatch near the vent just in front of the radiator. For those models with horns mounted between the first and second radiator fan, the air line should follow the path on the model but end at the rear of the dynamic hatch. For those with cab mounted horns like this model, the air line should not continue to the point between the fans.