Auto Air Horn Installation - Wiring

I am installing an airhorn in my 1946 Diamond T pickup truck but need help in understanding how to wire it correctly.
The two horn trumpets and compressors have already been installed
correctly. It's the electric wiring I need help with. The kit comes with two sets of terminals to wire the compressors and horns to the truck's electrical system. I've had no problem wiring the compressors to the 4-post terminals and grounding the compressors to the chassis as instructed.
What I'm confused about is how to wire the other three posts on the two terminals. I have a wiring diagram that I have posted as well as a photo of the wiring that runs from the present steering wheel column and horn button. The truck's horn wiring is already installed from the steering column but there is no old horn to remove. I am near certain the horn wiring from the column is properly connected to a junction box which in turn is connected to the 30 amp fuse in the fuse box. But how to "intercept" this wiring scheme already in place and connect it up to the terminals provided with the horn kit is what has stumped me. Thanks. View the attachments for this post at:
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