1973 Dodge Dart Sport Number of Horns

I just got a 1973 Dodge Dart Sport and am working of getting the horn to work. I got two horns with the car and the wiring harness (new) for the horns has two wires for two horns but there is only one slot for one horn. I have a picture from MOPARS in the Park of a 1973 Dart Sport and it does have two horns.

Can anyone explain what's up with just having the one horn?