See the attached. Follow the yellow line. It eventually leads to P403, pin 5 as the source for 12V for the parking brake signal.
By other drawings I have, fuse F14 on the Front Distribution Panel (FDP) feeds P403, pin 5. It's a 5A fuse. I would start by checking the fuse and- if it's OK, whether or not you have 12V on its inlet side.
You'll find the FDP by opening the front-most storage bay on the driver's side, and opening the large plastic box you find there. The innards should look like below. You can ignore the red circle (for this problem). Fuse F14 should be 14th from the right on that long row near the top.