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I'm not going to claim that I'm the world's best documenter, or even that I'm a good one. However, my scientific training instilled in me a high regard for the integrity of documentation; if you make it, then it should be as close as absolutely possible to whatever it is that you're documenting.
And so it always facinates me when documentation is sort only sort of vaguely resembles what it is that it's describing. A couple of days ago I went looking for the wire that leads to be beetle's brake lights, so that I can measure the total amount of current that they draw. First, I found the relevant part of the wiring in the wiring diagram:
The important thing here is the three-wiring coupler. Generally speaking the wires going up on the diagram are going down in the luggage compartment of the car; most of the wires coming out of the top of that coupler go down to the pressure switches on the brake master cylinder. The wires on the right are black, indicating that they are at battery voltage when the key is on, but not otherwise. The black wire with the yellow tracer goes from the black wire to the horn.
I didn't include the whole diagram, but the black wire with the red tracer goes into the wiring harness and back to the brake lights. I've circled the wire in the diagram. I just need to find this connector, find the black wire with the red tracer on one side of the triple connector on the opposite side and opposite end as the black/yellow wire.
It is said that "theory and practice are closer in theory than in practice". No exception here.
To get oriented, here's where we're working.
This is taken from the right side of the luggage compartment looking across to the left side. At the upper right of the photo you can see the signal light on the left front fender. To the upper left is the brake fluid reservoir. At the bottom the black part is the left edge of the fuel tank. I've circled the triple coupler where it sits on the inside part of the fender. The wiring harness goes up to the left.
Here's a close-up, with my test lead already wired up.
The black/red wire is the center of the three, not one of edges. And interestingly, the black/yellow wire is on the OTHER side of the connector and goes into the wiring harness. I guess at some point they decided to connect to the + horn wire farther up the wiring harness, so it made sense to switch the side that the horn wire connected to, but that change didn't make it to the diagram.
So I found the correct wire, and I used the diagram to do it. However, whatever procedure was used to wire this car, the wiring diagram wasn't taken directly from it. By the way, the wiring diagram photo was taken from Bentley, but I did wander downstairs and double-checked the official dealer wiring diagram; it's the same.
By the way, the brake lights draw 3.87A at 12.7V. Plenty of overhead for an LED 3rd brake light.