Internally routed dynamo taillight not turning on

I've set up rear dynamo lights before and have soldered wires and whatnot before but this dynamo setup is a little different and the tail light won't turn on after connecting the head light (which does turn on)

For this setup, the tail light is mounted to a threaded braze on on the back of the seat tube (like this Rene Herse tail light is) so the wiring for the taillight is internally routed through my frame and fork. The framebuilder routed the wire for the tail light through the frame and fork for me.

What I've done is I bought the tail light linked above, then soldered the wire coming out of the tail light to the wire the framebuilder routed out of the back. Then at the front, I simply crimped on one of those small spades that goes into a SON Edelux II headlight.

I just need a gut check that I didn't do something obviously wrong here? Unlike other SON tail light setups I've done where there's a ring terminal involved, the wiring coming from the tail light and routed through the frame was not a coaxial so I figured this must mean it's grounded through the frame?

I noticed that internally, where the down tube meets the head tube, there's sort of a nipple that protrudes into the headtube (which I believe is connected to one end of the tail light wiring that goes down the down tube toward the rear). The steerer tube has a metal plate (I think it's copper) welded to it just about where it would meet this nipple and the wiring going to the front comes out of the bottom of the fork crown so I'm guessing this plate touching the nipple in the headtube is how the front wiring is connected to the rear wiring.