hazaa;
Normal Horn wiring is that the wire coming up Steering Shaft is a grounding wire at Horn Switch to activate Horns.
If you want to run an addition wire with power to your Steering Wheel for something which needs continuous power, there is no reason why you couldn't route a second wire up from Steering Box, around Hardy-coupler and to St Wheel...just make certain it is properly fused.
Cheers
Reference info:
http://www.sw-em.com/122_horn_notes.htm