Of all of the electrical circuits in a VW Beetle, the horn (specifically the ground) circuit seems to give people the most trouble. The horn receives positive power from the fuse box as soon as the key is turned on. When you press the horn button, the ground circuit is complete and the horn turns on. The ground circuit wiring and components change throughout the model years. We've put together 4 different diagrams to help you when trouble shooting your horn on 1954 to 1959, 1960 to 1967, 1968 to 1970 and 1971 to 1979 Beetles.
First things first when testing your horn wiring is making sure the horn is actually hooked up and then that it is operating. The 2 terminals on the horn are not positive or negative specific, one terminal should have a black wire with a yellow stripe, the other terminal should have a brown wire. With a test light, verify that the black and yellow wire is "hot" (receiving positive power from the fuse box). If it is not, check the wiring and fuse at the fuse box. Once you've verified that the horn is getting power, use a test lead (a piece of wire with two alligator clips at either end) clipped to the brown wire on the horn. Then touch the other clip to the horn bracket mounting bolt (or other suitable chassis ground). The horn should honk, if not, your horn needs to be replaced.
You can now test the ground circuit with the help of an assistant. Hook up one lead of a test light to the brown wire and touch the positive side of the test light to the black and yellow wire. Then have the assistant push the horn button on the steering wheel. The light should come on with the button pressed. If not, you'll have to investigate further.
1954-1959 VW Horn Wiring Diagram
1954 through 1959 Beetles the ground circuit starts at the steering box to coupler joint which is grounded past the rubber steering coupler with a ground strap, grounding out the metal steering shaft.
When the horn button is pressed the ground signal is completed from the shaft, through the horn button and wire which is attached to the horn button. The horn button wire runs to a copper sleeve on the steering shaft which is isolated from the steering shaft. The steering column housing has a carbon brush which presses against the copper sleeve. A brown wire on the brush is routed from underneath the dash, into the trunk and down to the horn and completes the circuit when the button is pressed.
Make sure that the horn button clip and the area that the clip sits against inside the steering wheel is not painted over or corroded as the button needs to ground against the steering wheel to complete the circuit.
1960-1967 VW Horn Wiring Diagram
1960-1967 Beetles the ground circuit starts on the steering box side of the steering coupler where a brown wire is attached to a coupler through bolt. That wire feeds past the rubber steering coupler and is run through the center of the steering column. At the steering wheel, the wire is mounting to the chrome horn ring.
When you press the horn ring down, the ground signal continues through the steering column tube, to a tab at the bottom of the tube. A brown wire connects there is routed into the car (above the pedal assembly on the bottom of the dash) then into the trunk and then runs down to the horn and completes the circuit when the button is pressed.
A few notes regarding the steering column tube, as it is part of the horn ground circuit, it is isolated from the body.
1960 and 1961 Beetles used plastic spacers and shims to isolate the tube. If those pieces are missing or worn, you will have to fabricate new pieces. The only other option is to change the tube and steering wheel to the 1962 through 1967 style.
1962 through 1967 Beetles use rubber mounting grommets (one at the firewall and one at the upper steering column bracket) to isolate the tube. If the steering column tube is not isolated, the horn will honk constantly.
1968-1970 VW Horn Wiring Diagram
1968 through 1970 Beetles models the ground circuit starts on the steering box side of the steering coupler where a brown wire is attached to a coupler through bolt. That wire feeds past the rubber steering coupler and is run through the center of the steering column. At the steering wheel, the wire is mounting to the chrome horn ring.
When you press the horn ring down, the ground signal continues through the steering column shaft to and isolated steering column bearing with a brown wire soldered to it. That brown wire runs down the steering column, under the dash and into the trunk. There is is connected to a brown wire from the left headlight harness with a shrouded connector that connects to the horn and completes the circuit when the button is pressed.
1971-1979 VW Horn Wiring Diagram
1971 through 1979 Beetles the ground circuit starts with the steering column itself. It is not isolated nor is the steering column bearing, making the steering wheel itself grounded. When you push the horn button the ground is sent through a wire to the contact ring which is bolted to the bottom of the steering wheel car. That ring contacts a contact tab on the turn signal switch which is connected to a brown wire. The brown wire runs into the turn signal switch wiring conduit which runs down the steering column.
At the bottom of the steering column the conduit connects to the turn signal steering column harness and plug which runs into the trunk. In trunk the slightly larger gauge brown wire (there is a smaller gauge brown wire as well which is for the headlight relay circuit, not the horn) connects with a shrouded connector to the brown wire from the left headlight harness that connects to the horn and completes the circuit when the button is pressed.
With the above information you should be able to track down any issues you have with your horn's electrical system. Most importantly, you can get the issue fixed and get your horn operating properly so you can give a friendly honk whenever it is needed!