Pleased I could help.
when I use a fluke meter on it the black & red beep out when you push on the horn button,
This isn't clear ...
If you've a Fluke meter and definitely
the "horn button"-'n'-"dimmer switch" I pictured in my previous post:-
. First ensure the horn doesn't 'ground' through its mounting - measure between the mounting and each terminal in turn, you hope to see thousands of or infinite Ohms; if there's any continuity between the mounting and either terminal, the following won't work.
. Connect between the existing Brown/Blue (NU) wire and one horn terminal. If the back of your bike's ignition switch looks like this:-
... and the horn's in the standard T100 position between the frame tubes above the engine and under the front of the tank, maybe connect from the unused ignition switch terminal beside the Brown/Blue wire to one horn terminal?
. Connect the existing harness Purple/Black (PB) wire to the other horn terminal. Do not
connect a Red wire to any horn terminal.
. Connect the other end of the harness Purple/Black wire to the wire in the horn button/dimmer switch that isn't used by the headlamp. If the switch you have has 'correct' wire colours, the pre-'71 horn button wire is Brown/Black (and the other wires are Blue/Red, Blue/White and plain Blue); otoh, if the switch is the more-common shonky crap, an educated guess says the horn button wire is plain Black (and the other wires are Yellow, Green and White)?
. Bear in mind the electrical return path from this horn button to battery +ve is through the switch body, its screws into the handlebars and then some indeterminate sets of contacts between sundry other bits of bike; if you think that sounds less-than-ideal ...
Best improvement is: identify where the horn button makes contact with the switch body, connect a (Red?) wire there, route it alongside the other wires to/from the switch and connect it somewhere unobtrusive to the existing harness Red wires.
Failing that, a (Red?) wire connected between somewhere near the switch and the existing harness Red wires?