When I brake harder than I usually do my horn blows. The folks in front of me think I am honking for them to go What the heck. Anyone know how to fix this problem?

 

Year? Model? Aftermarket steering wheel?

 

Stop braking?

 

Are you braking so hard that your chest is against the wheel?

I'd bet that the horn pad/ button is the issue. Remove it and put some electical tape over the connector and drive it a bit trying to repeat the hard braking. If it still does it, then you have a short in the wire to ground elsewhere, probably where it goes through the firewall, etc.
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The springs that hold the horn pad back have sagged a bit. If you are stationary, is the horn a very light touch to sound?

Take the horn pad off and stretch the spring/s a bit to make them slightly longer.
Alternativly put a bit of foam b/w the pad and the wheel so that you must squash that before the horn works.

 

Check for a wire with damaged insulation behind the brake pedal arm (this happens in 993's at least)