THANK YOU. i appreciate all of this and will get to work. i will also crack my electrical manual and review the toyota document which didn't seem to print properly for me last night. i appreciate the opportunity to make more headway with this topic!So I wrote all that without looking at the circuit diagram, so here a few nuggets:
The connector (C14 on the EWD) terminals 9, 10 are for the horn circuit. This connector is tucked under the column. Terminals 9,10 in the connector are the connection to ground. FWIW, the terminals in the connector are numbered to to bottom, left to right in the female half (the male is opposite). If the connector diagram has a X in a terminal spot, there's no conductor/terminal there. A dot means there is. The convention Toyota uses in these EWDs is the terminals in the connectors pertinent to the circuit you are looking at are numbered. These numbers correspond to the circuit diagram.
The ground, for this circuit, is behind the plastic kick panel cover, next to your left foot position when driving. It woudn't hurt to remove the scre, clean both the sheetmetal panel and ring terminal and reassemble. You can check the ground by connecting the other end of that wire to your DMM and the ground lead (of the DMM) to another screw in the panel somewhere. If you have a good ground you'll see it (or hear it, depending on your DMM).
The other information on the bottom of the page refer to the groundpoints, connector joining and relay diagrams, which are also handy to have. They are in the EWD; look for it in the Resources section.
Since you have observed the horn/warning flasher is on the same circuit, and the flashers, relay and horns work, the problem is probably limited to the horn circuit between the steering wheel and the ground at the kickpanel.