Electrical Help Buss Bar

[WNU]

Hello everyone! I'm a novice and need some advice on the wiring of my '66 D100. I am using the original harness that I have mostly repaired from years of rat damage and am getting pretty close to having things in running order; lights work (exception of dome light), engine turns over. My question is what powers the buss bar in the instrument panel - still no power when the key is "on"? The two hots are to the AMP Guage. The only wire that I have that is "hot" when the key is on is a black one coming out of the harness under the dash. This was one of the wires rat-eaten that I repaired...just never knew what it went to? Is it possible that it goes to the black wire on the Voltage Regulator, or back to the buss bar? I have the laminated wiring diagram by ClassicCarWiring, but am not clear on this. My intention is to run an electric fuel pump (w/ in-line fuse) and electric choke off the buss bar.
Thank you; assistance is very much appreciated!

[Series1Utiline]

Others more knowledgeable than me will know the specific routing and colors. The buss bar power comes from the driver's side inner fender mounted relay and is fed through the bulkhead connector next to the driver's side hood hinge. When you disconnect that, the power lead is the large red (10 gauge I believe) wire. That lead goes direct to the Amp gauge buss bar and then (amongst a few other branches along the way) goes to the ignition switch.

[sledgehammer]

I’ve had my ‘68 apart for 2 years and got it together now but also have no power to the bus bar.