Hi there I'm attempting to reconnect my horn wiring which is currently re routed to an awkwardly located switch
Where would I find the connecting point on this steering wheel setup?

Thanks

 

The trim panel you have removed has buttons on it. When you press one or another it earths the circuit to those silver-coloured posts on the wheel spokes. The 12 volts comes up the centre brass thingy on top of the column on the large plastic hexagon. If you take a piece of wire an jump between the two the horn will sound, ignition on.

 

Currently the wires for the horn are routed to a switch under the dash board. Surely I need to take those wires and attached them to the steering wheel?

 

That was not clear in your post. There should be a copper wiper touching a space in the lower column, receiving a 12 volt feed from the horn relay. This must be reinstated for the horn to work as OEM. Do an advanced search on the XJS horn circuit you will find loads of stuff, pics, etc etc.