Not been here for a good few years but still have my GTI and trying to get it through the MOT due to a couple of niggles!!
Failed on horn not working which cause me to do loads of wiring checks inc removal of fuse box. Now it’s all back together when I switch on the high beam the headlights go off ! I also have no flash. It was working ok before I had it apart.
Following going through all the similar threads on this site I have confirmed the relay (far left) in the fuse box is working by swapping it with the electric window one and then swapping back, and also changed the relay near the expansion tank and confirmed it is working. I have also fitted a new indicator stalk.
I suspect the one thing that MIGHT be contributing is the loose wire that I have found when going back to the fuse box! It is stamped 6J and has a single plug on it but I can’t for the life of me see where it connects to nor can I even find it on the wiring diagram. Any electrical gurus help?
The fracture causing the intermittent horn will get worse until it won't make contact at all. My incredibly bumpy road has proved that.
If you have checked continuity from stalk to fuse board and all is OK it is likely a break in the board that is stopping your headlights from working.
For the headlights it might pay to check that the three fuse joints ringed in red have contact with each other and that there is continuity to R7 (also ringed)
The outlet fuse joint for #11 is inverted compared with #12 and #13.
Remove the fuses to test as that isolates the line from the circuit. Meter test from top side for continuity if still installed. Right to left on top, left to right on underside for numbering.
With the board disconnected from power try jumping a wire between those points to see if it changes things. If so, run wire across and tack down to the board with epoxy to prevent shaking after you have soldered it into the circuit.
I ran a wire from R7 to fuse point #11 and it sorted my problem with all the lights.
You can see from the diagram how the three fuse lines interconnect. This seems to be where the breakdowns occur.
Images show plug codes on the fuse board, input/output blades numbered and fuse circuits, and marked locations of fuse output sides and blade R7. Also 309 diagram with input and output wire codes (should be similar to 205)
I can't see a 6J. The only single wires going into my board are a blue and a white that both plug into socket U.
I hope some of this info helps you.