I have some time before having to leave too - wife is not here yet & we are riding together.
I think of electricity as "water" and the wiring, relay, etc. as the "plumbing" for a system. If the pipes break, or a valve doesn't open or close when it should, then you have problems. The hard part is identifying the right parts and know what to look for. That is basically what we have been doing so far.
I think that socket pin that was "dead" is the input signal from the horn switch (button). When the horn button is pressed, that pin should be connected to Ground, through the switch and connected at G201 (from the schematic). I also noticed that is a "splice" between the Ground point (G201) and the connector going to the horn switch (C204). C204 might be the next point to find to see if Pin D is connected to G201 (probably is) and that Pin G is switched to ground when the horn button is pressed. If you have a good connection to ground at Pin D and Pin G does NOT switch to ground when the horn button is pressed, then there is a problem between that point and the horn buttons.
Unfortunately, I do not have diagrams for where these connections are, but I do have descriptions.
C204 - Below Instrument Panel, Right-Hand side of the steering column
G201 - Below Left-Hand side of Instrument Panel, on the Left-Hand Kick Panel
S203 - Instrument Panel Harness, Lower Left-Hand side if instrument panel, Left of Steering Column
If you can find the C204 connector, then see if you can check out Pin G and touch it to a good ground (like before).
If you have an ohmmeter, also check that Pin D is connected to ground.
If all of that is good, and the horn does not sound when you press the button, we have found the problem area (probably the horn switch or wiring to it - from C204 and up through the column).
Please let me know when you get a chance to test this out and what you find.
Take Care, Greg A.
P.S. Wife is home now & I will be gone in a few minutes.