Hi Sondre. So on the GU50 the signal wire central conductor is what carries the signal and it gets attached to pin 2 on the GU50 socket. On that end of the signal wire, the ground is cut off and not connected to anything. On the other end at the driver board, there’s a “Signal Out” blue junction. The central conductor that carries the signal goes to the positive terminal, the ground shield goes to the negative terminal and it will have a path to ground from that point through the board and the black lead that then goes to the star ground.
One of the differences that you might be noticing with the prototype is that R7, which is a resistor that goes to ground, used to run directly from the GU50 pin 2 to the tag strip, and then to ground. That resistor was moved to the new driver board to make assembly easier.
I hope that clears things up. Let us know if you need more clarification.