Dissasemble drivers side plastic panels at front of door, & under the steering
wheel by pulling them off.  Pull carpet back towards drivers seat.
(Sorry no pix of the disassembly process)

Mount horn as shown

Get some lightweight speaker wire, and attach it with electrical tape to either a thin flat blade
screwdriver or a cut wire coat hanger and shove it through hard in this grommet from the
engine bay side.

Connect this wire to the horn wires., then the wire through the firewall can be routed up inside
the dash to the center console area, or wherever you want to mount the control box.  I drilled
a largish hole that fit a rubber grommet I found in the autoparts store and then cut a slit in
the grommet to fit the horn wire, and the power and ground. (hole in the cubby box)

I then extended the power and ground wires from the control box through the same hole
and down to the fuse panel.  Wiring it up like this.

Always use an inline fuse as close to the power source as possible.  I used an empty switched
circuit and made a plug to go into the fuse connection (you can buy a fuse tap, I just was
too far along to do that)  Ground works well at that screw I show.  The car has it's
underbody lighting, the GPS theft guard device and now the horn all coming from this box.

Finished looks like this:

tidy up the wires and button the panels back up.