Mission Accomplished...thought I'd add some notes for people searching for this in the future:
1) On the tail light, there are three connections:
Red: powered only when brakes engaged
Yellow: powered all the time when key turned on (use this one for GPS power)
Black: on the side (the red and yellow are below), this is ground
2) I looped everything on the right side, using zip-ties to put the gps power cord alongside other cable routes.
Pics below:
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