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.

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