Just found this if it helps
Look at these wiring diagrams https://www.thesamba.com/vw/archives/in ... nBrake.jpg https://www.thesamba.com/vw/archives/in ... lights.jpg
keep pin 58 on the rear as a tail light feed, pin 54 feed (black/ yellow and black/ red) take from the rear light unit and connect to the reverse light (reverse feed wire disconnected first).
Run a wire from front to back, at the rear connect to now available pin 54 (stop light) and piggy back to the opposite light.
At the front is where the 68 wiring diagram looks different to my 71, mine has a hazard switch which i removed the feed from the brake pressure switch (pin 54), i connected this to the new feed to brake lights.
On the 68 wiring diagram if you look at item J (flasher relay?) try removing the green wire to pin 54, the one which is fed from items J1 and J4 and connecting this to your new brake light feed.