[T3] Invasion prep

[jadney at vwtype3.org]

On 22 Jan 2026 at 13:27, Max Welton wrote:

> Jim, disconnecting the horn in this case means disconnecting the
> positive wire at the horn.

Good, this means that the problem must be IN the horn or in the ground side 
of the circuit.

> The horn wire is connected as it should be. With everything connected,
> the horn sounds when it should.

Seems odd, but we may find out later why it's working this way.

> If, however, I remove the ground strap from the battery, I measure 12
> volts of potential between the battery terminal and the strap. This
> goes to zero with the horn disconnected at the horn.

Interesting test, good data. Following that lead, here's what you can test 
next. Put the + wire back on the horn and disconnect the brown ground wire. 
Measure the voltage between the - horn terminal and the brown wire.

If you measure ~0 V, the problem is in the horn. In that case, you could 
remove both wires and measure the resistance between either terminal and 
the horn body. It should be infinite. I've never seen a horn problem like this, 
but anything's possible.

If you measure ~12 V, the problem is somewhere in the ground circuit wiring 
between the horn and the steering column. 

In the latter case, I recommend that you measure the resistance between the 
disconnected brown wire and the body. If you have a second person 
available, have them watch your meter while you wiggle wires. They should 
see a change in resistance as you get close to the problem.

> One thing to note is that due to the front beam being freshly
> powder-coated I ran a ground wire from the steering box to the
> chassis. Without that, the horn wouldn't sound at all. I've run
> similar grounding wires for the rear signals and the fuel sender.

There is an OE brown wire that jumps from the steering gearbox to the top 
bolt for the clamp that holds the beam to the pan horns (not the horn that's 
on topic here.) That wire is necessary not because of paint on the beam but 
because the rubber beam mounts keep the beam electricaly isolated from 
the body. Yes, if it is not installed, the horn won't work.

If the horn checks out okay, there must be a mild short between the brown 
wire that returns to the steering column and ground. It's important to 
understand that there are two halves to the ground side circuit. The "hot" half 
runs from the horn up to the TS switch on the steering column. The "cold" 
side runs down the inside of the steering shaft to the steering gearbox and 
then to the pan (ground.) The horn button in the center of the steering wheel 
is what separates the two halves.

The wire that goe down the steering shaft is not the problem, as that's on the 
"cold" (always grounded) side of the horn switch contacts.

It seems likely that this brown wire, that goes up with the other TS wires, 
must be pinched or abaded somewhere. It's important to find it, because it's 
likely to be a full short eventually.

The problem could also be in the horn switch itself. The horn contacts are 
part of the center of the horn ring at the center of the steering wheel. The 
horn ring is mounted/suspended by 3 shoulder screws with insulators and 
springs. Under each shoulder there should be an external star lock washer. If 
one or more of those lockwashers is left out, the horn will tend to honk 
randomly. It's also possible that if left out, there might be a poor contact 
there that drains the battery without sounding the horn.

Sorry, this was long and, as I said, complicated.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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