Let's make sure we're on the same page. What year is your car and does it have factory gauges (factory option or or did you add them?)
My '68 is as follows. I have add-on factory console gauges.
10ga red from main harness to junction block. This goes to the horn relay, alternator, and voltage regulator.
14 ga black that turns into 20ga orange fusable from main harness to the junction block. This goes to the console amp gauge if so equiped.
20ga black from the headlamp plug to ground.
On my relay, working from left to right as the relay is mounted in the car:
LH screw lug:
10ga red and 10-12ga black mounted to the LH screw lug.
RH screw lug:
Orange fusable link and black fusable link both mounted to the RH lug.
However, the 1968 diagrams are not good. There is no horn relay detail like that for 67 and 69. I would think they would be similar.
To see a picture of my car http://www.geocities.com/casanoc