Most model As have three wires connected on the output side of the cut out. One is the charge wire for the battery that connects to the terminal box left side terminal. Of the other two that share a terminal, one is the horn power and connects directly to it. The other is the power wire for the light switch and connects directly to the switch terminal plate. This is a good link with photos and illustrations from MAFCA.
https://www.mafca.com/downloads/Semi...ex%20Janke.pdf