71 bus horn

[doug-ocon]

I am working on bringing a 71 bus back from the dead . a couple of weeks ago i worked getting the horn working. Replace the horn, rehooked the ground at base of shaft ..wired button at steering wheel ... BEEP BEEP all good .

Then I whent to start the bus and as soon as the key went in ....BEEEEEEEEEEP!. REached under the bus an pulled the wires.

the ignition switch has been replaced ... I am assuming it is grounded some how ... but through the Key?

Any thoughts

[mikewire]

Horn shouldn't sound just by placing the key in the ignition...you should have to at least turn the key to ON for that.

Something else is going on with the horn circuit...I would suspect you have a wire connector or a bare wire somewhere touching and grounding out.

Have you searched around for the horn circuit diagram? It's also in the Bentley.
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@countdowngarage
@bigskyeuro

1972 VW Kombi 9 Passenger Deluxe w/ 2.0L F.I. VWAC swap
1965 VW Beetle Deluxe Bahama Blue

[airschooled]

Saying an early bay horn can be fixed by looking in the Bentley is like saying you can build your own microscope be reading an optics textbook: possibly true but nobody can actually do it. The wiring is much more subtle than the diagram gives on.

doug-ocon, are you saying you have the horn functioning with the key off? This sounds wrong, as the horn should be fused through #10, which only gets its power from the ignition switch.

Check the new ignition switch for a small-ish grey wire. Where's it going?

Robbie

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[mikewire]

Robbie...no, I wasn't referring to the wiring diagram, although you could if you wanted to torture yourself! I was talking about this horn diagram, found if you search, and also in the Bentley:

I fixed my horn using this diagram, very helpful.
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-Mike

@countdowngarage
@bigskyeuro

1972 VW Kombi 9 Passenger Deluxe w/ 2.0L F.I. VWAC swap
1965 VW Beetle Deluxe Bahama Blue

[aeromech]

Who needs a horn these days? I’m sure there’s an app
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[Starbucket]

Mount your horn pointing to the rear because there will never be anyone in front of you to honk at, this way you can honk back at the line of cars behind you. Check the spade connecter at bottom of steering column with meter and see if it is grounded without pushing horn button.

[mserino]

I have a related question on this. On mikewire's post it shows a good picture of the circuit with the steering column tube isolated from ground and connected to the horn. The steering column comes in contact with the tube at the (number 3) steering column bearing. Would your horn not sound if you placed a ground anywhere on the column?
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[busdaddy]

The bearing is insulated in a rubber bushing.
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[mikewire]

[telford dorr]

Every metal part of the steering (column tube, shaft, turn switch housing, etc.) is "hot" with power from the horn. The only thing which is grounded is the wire coming up through the steering shaft. Now, theoretically, the steering lock could ground the steering shaft, but by that time the ignition switch is already off, cutting power to the horn.
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[mikewire]

[telford dorr]

Every metal part of the steering (column, shaft, turn switch housing, etc.) is "hot" with power from the horn. The only thing which is grounded is the wire coming up through the steering shaft. Now, theoretically, the steering lock could ground the steering shaft, but by that time the ignition switch is already off, cutting power to the horn.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[mikewire]

[SGKent]

if one part of a conductor is "hot" it is all hot. You need to rephrase your question because right now the question is like you are asking what part of the ocean is wet.
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[mikewire]

[telford dorr]

Upper support bushing / collar and spring (1,2, 3 in diagram above).
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[kreemoweet]

The shaft is connected electrically to the column tube (which is hot when the ignition is on and horn button not pressed) via the bearing, which is metal thing in contact with both the tube and the shaft.

But the hotness of the shaft is incidental - what really is meant to be hot is the steering wheel metal. The bronze spring
under the wheel maintains firm electrical contact with the bearing (and therefore with the hot column tube).
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[Starbucket]

[busdaddy]

[SGKent]

So

The schematic shows that fused 12V+ goes to the horn. Looks like off fuse 10

Then when the horn is not grounded by the horn button, there would be zero amperage going thru the horn into the column which is isolated by the plastic ring at the bottom and bushing at the top. However the 12V+ would still go thru the horn and to the same spot so that the column was hot with 12V+. If you measured it with a VOM, it would show 12V+ hot because the VOM isn't pulling any electricity so the horn has no amperage to drop the voltage. It is only measuring the voltage difference, like water pressure in a water line.

When the horn button is pushed to sound the horn, it grounds the column thru the button and the column would now be at ground so the voltage on it would read no volts and the horn would be sounding.

If you tried to run a stereo off the column, the horn would be in line and any amperage on the way to the stereo would pass thru the horn. That resistance would lower the voltage passing thru it because it was using amperage. The horn works just the same as a light does. It uses that electrical energy passing thru it to do some other form of work. If you for example were to hook 12V up to one side of a light you were holding in your hand, and measure the wire, it would read 12V. If you read the other terminal on the light it would also read 12V. But as soon as you hooked a ground up the light would glow and the voltage on the ground side would go to zero as the light used up the energy.

If you are still confused look at it this way. You have a wire in your hand coming from 12V on the battery. You hook it up to the horn. No sound. You hook another wire up to the other side of the horn but hold it in the air. No sound. You measure the voltage on the first side of the horn. 12V is the reading. You measure the voltage on the wire you are holding in your hand, 12 V is the reading. You now ground the wire in your hand, the horn honks. While it is honking you measure the voltage on that wire now. It is zero on the ground side and 12V+ on the 12V+ side. The column is like the wire you are holding in your hand. It is hot until the button grounds it.

The horn button is a push to make contact switch. VW could have run two wires to it, one from the horn ground and one to the auto ground, so that when you pushed it the horn honked. Instead VW used the column as one of those wires so they only had to run the one wire to the horn button.
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