Fixed it after ruling out component and wiring issues while picking through the FSM.
Apparently while "borrowing" a fuse from a good circuit (horn) to fix the aforementioned blown tail light fuse; I didn't replace it within the fuse holder in front of the battery. Being I found the horn circuit is powered from two sources, I only had half the design voltage. This explains losing half of the battery voltage over the halo controller fuse once it began drawing power.
Glad it was a simple solution requiring little elbow grease but nonetheless time consuming due to neglecting the detail of returning a fuse to the borrowed position.
