Fixing the Horn
One day that was much longer ago than I care to admit, the Beetle's horn stopped beeping. I finally took a weekend to learn about the horn's mysterious wiring only to discover that the problem took three seconds to fix - a connection had just become corroded.
Our story begins here, with the back end of the fuse box. The real story starts with the battery, of course, but the part we're interested in starts here. Toward the middle of this picture are a few thick black tubes carring wires, and one of them has four wires coming out: a black/yellow, a yellow, a white, and a brown. That's the tube we're concerned with, and the black/yellow and brown wires are the two we care most about. In the beginning (once the key was turned to 'On'), there was power. The power was good, and it flowed through the fuse box and into that black/yellow cable. From there it entered the black sheathing and disappeared into the depths of the luggage compartment.
Eventually the black/yellow cable (and its contained power) emerge here, at a connection onto the horn. The horn is easy to find: just stick your head under the front left fender. If you have trouble finding it, have somebody blast a note from it while you're looking. Anyway, the black/yellow cable carries power into the horn and back out the brown cable on the other side. That brown cable then works its way up the original sheating and back into the luggage compartment.
"Woah there," you say. "You've got that backwards. You just claimed that the horn is hot. Everybody knows that electrical devices are switched on the hot end, so you must mean that that black/yellow cable is the ground." In a normal world, that would be correct. But remember, those wiley Volkswagen engineers liked to reuse things as much as possible. You can get the whole story here, but the short story is that the simplest way to wire the horn button on a rotatable steering column is to switch the ground side instead of the hot side. Now back to the tour.
We're back up into the luggage compartment again now. This time we're interested in the brown (or maybe orangish in this picture) cable coming up from the black sheath. It runs off to the right, through a plastic junction box, and then through a hole and (off-picture) in to the driving compartment of the car. It is still carrying positive current at this time.
That little brown cable makes its entrance here, coming down from behind the dashboard and wrapped up with other cables in more sheathing. It drops down and then scoots its way into the steering column as seen in the bottom-center of this shot. Once inside, the wire connects to a commutator that brings the entire inside steering shaft up to positive potential.
We're nearing the end of the tour now. This is a shot of the center of the steering wheel with its little button removed. The silver ring in the center is the middle of the horn ring. Note that the brown cable seen here is not the same one seen previously. That other one terminated with the hidden commutator mentioned with the previous image. That wiring job made the inside of the steering column one giant terminal for the horn button, and what we see here is the other terminal. When the horn ring is pressed, the whole assembly seen here moves down and makes contact with the hot steering column. Since we now know that we're switching the ground, we can safely assume that the wire seen here is now headed off to ground itself someplace. But where?
This brings us to the final stop on our tour. Here we're looking at the rather dirty area beneath the gas tank where the steering column passes through on its way to the steering gearbox. That's the steering column coming in from the upper-right corner and exiting toward the center-left. The big fat disk in the middle of it is an insulation disk keeps the hot steering column isolated from the grounded steering box. The dirt-colored wire seen exiting the steering column tube is the same brown wire we saw heading down the center of the steering column in the last picture. Here it exits the tube and, using one of the bolts as a jumper through the insulating disk, grounds itself through the steering gearbox. What a trip it has been!
And now for the part where I fix the horn: in my case, that very last wire connection (the one connecting the brown wire to the jumper/bolt) was just corroded and needed cleaning. Had I started my fixing on this end of the circuit, I would have been back honking at people in no time. However, I instead started on the other end and troubleshot the entire length of circuit before finishing here. At least it makes for a good story!