horn circuit

I have been following a wiring chart for the 72 Demon and have no power to the large yellow wire running up to the ignition switch. I ofcourse put the seats back in awhile ago and can't get under the dash enough to see where it runs. The yellow comes from the coloum to a connector the yellow from the other side up into the dash. What I can't tell from the chart is what feeds this wire the power? It should be live at all times I would think. I will check the horn relay as well.
Thanks
AL