Horn Circuit Ground Fault

Are you using a relay?

Yes a relay was installed.

Jason

The relay was part of the problem for me, at least that seemed to be the consensus.  The leakage to ground was just enough to keep the relay latched once closed, but not enough to close it without encouragement.  Finding and solving the problem would have most certainly entailed a full weekend (or three) of many frustrations so I decided to sacrifice a few dB and just ran my new horns without a relay.  Problem solved.

I wonder if a diode or two might have solved it?  @DannyP or others might chime in.

So far my resolve has been to remove the relay and disconnect the second horn. Indeed there is a miniscule grounding where there shouldn't be.  I confirmed this with my multimeter. The unintentional ground must be somewhere in the wire that runs between the horn button and the horn.  I'll look for it tomorrow.  If anyone has any ideas on specifically  where the fault might be please shout out.

Jason

How does VMC ground the horn wire to the relay?  Is it a direct wire that runs down the column and flops around the rag joint or ???  Do they use some sort of horn contact?  

@chines1 posted:

How does VMC ground the horn wire to the relay?  Is it a direct wire that runs down the column and flops around the rag joint or ???  Do they use some sort of horn contact?  

VMC does not use a relay to power the single horn. I added a second horn and installed a relay to accommodate the additional amperage draw.

I'm thinking that the steering column may be inadvertently grounded somehow.  The ground fault is not sufficient to power a horn sans relay, but is adequate to trigger a relay when instlalled.

Jason

I installed a relay from Advance Auto Parts many years ago when I swapped the single for a dual horn set and never had a problem. I agree with you that you might have a problem with the grounding in the steering column. A friend has a '67 Bug that he refurbished and it had the same problem with the stock single unit. It's most times that single wire that runs inside; sometimes the wire insulation gets pinched or chafed and then the thing makes contact.

As I recall, there are a couple of different horn grounding methods used by VW over the decades.  The later version totally isolated the entire steering column (the outer sleeve) from ground and used the steering shaft as the ground source (with a jumper across the rag joint at the steering box to ground through the box to the chassis).

Often, the steering column can pick up a partial ground (high resistance, not a dead short) from one of the mounting fasteners.  Removing the mounting bolts one-at-a-time can sometimes point to the bad one and then you need to see what is touching and what you need to correct it.  Nylon washers and bushing are your friend, here.

The original horn is nothing more than a primitive relay that requires X amount of current to activate it.  The new relay you installed requires a lot less power to pull it in and, once it is pulled in, even less current to hold it closed.  THAT is your problem.

Two things you can do:

1. Find the partial short to the column and fix it, or:
2. Put a Band-Aid on it with a 1K half watt resistor (Brown-Black-Red-Gold) in series with the ground side of the Horn #2 relay coil wire to reduce the background current and allow the relay arm to release when the horn button isn't pressed.  I'm guessing on the resistor value - it depends on the current leakage to ground but that should be close to start.

Hope this helps.

----EDIT----

Just thought of another place to look - There is a special copper bearing at the top of the steering column under the steering wheel hub.  It is insulated from the column by a 2-piece nylon washer thingie but that provides part of the path to ground for the horn.

Good Hunting.

@Gordon Nichols posted:

The original The new relay you installed requires a lot less power to pull it in and, once it is pulled in, even less current to hold it closed.  THAT is your problem.

^
Agree.  The problem is not a dead short between the column and ground, otherwise the horn would always sound as soon as the ignition key is turned.  My issue, and likely yours as well, is that the resistance between the steering column and ground is low enough to allow a bit of current to flow once the key is turned on, and it just so happens to be enough to hold a closed relay closed.  The current flow is not enough current to close an otherwise open relay, and it is not enough current to sound the single meep-meep horn without the relay until the horn button is pressed.

I kept my two new horns and wired them without the relay and they work just fine.  They receive a bit less juice because I don’t have a relay, so I’ve likely sacrificed a few dB, but I suspect the loss is similar to what you would lose installing a series resistor with a relay circuit.

But by all means please hunt down the issue so we can all learn.  A beer is on me when you succeed.

@Gordon Nichols posted:

----EDIT----

Just thought of another place to look - There is a special copper bearing at the top of the steering column under the steering wheel hub.  It is insulated from the column by a 2-piece nylon washer thingie but that provides part of the path to ground for the horn.

Good Hunting.

Thank you for the well thought out response.

Indeed, the ground leak appears to be at the top of the steering column at the steering shaft to column interface.  I removed the steering wheel, steering shaft nut, spring and what I call a metal radial shim.  While everything was disassembled I "ohmed" the horn ground wire and no more leak!

However, I put it all back together and discovered that my ground leak was back.   A parts diagram of this particular area of the steering shaft/column would be very helpful.  If anyone has access to such a document please point me the way.

I like your resistor idea, which may be the easiest fix.

Jason  

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Just to make a complicated discussion moreso, I'll again note that I was in exactly the same situation, did the same thing, had the same mysterious problem, and solved it the same way.

One horn, no relay, no problem. Two horns, one relay, 'latching on' problem. Two horns, no relay, no problem.

So, it's about 2-3 years down the road and the lack of a relay has caused no issues. Keep in mind that, for most of us, the duty cycle of a car horn is about one second on, six months off.

But, in any case, these horns don't draw enough amps to make smoke or flames.

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@JasonC

I don't have a photo of the steering column innards, but I have a write-up I did for my personal service manual on how the horn works and will send it to you in a PM.

@Gordon Nichols posted:

@JasonC

I don't have a photo of the steering column innards, but I have a write-up I did for my personal service manual on how the horn works and will send it to you in a PM.

Thank you!

Jason

@Sacto Mitch posted:

. Two horns, no relay, no problem.

So, it's about 2-3 years down the road and the lack of a relay has caused no issues. Keep in mind that, for most of us, the duty cycle of a car horn is about one second on, six months off.

But, in any case, these horns don't draw enough amps to make smoke or flames.

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I wired a 1K resistor on the ground leg of my relay and couldn't get a peep out of my horns.  So out of desperation I tried  to operate both horns sans relay.  It's quite loud and seems to work just fine so far.

At some point I'll try other resistors, perhaps 750 ohms, with a relay to see if I can get it to work.

I certainly appreciated all the participation from the forum members on my topic.

Jason

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@JasonC

Jason, I just checked and it turns out I've had these (Hella) horns installed for five years now, without relays and with no problems. My car is a Kirk-era VS, and was delivered without a relay on the horn circuit (single, unbranded horn).

I do like using relays wherever possible on this car if for no other reason than to minimize wear on the contact points of the generally substandard switchcraft used throughout.

But as noted, the horn gets so little use that that's not really an issue. And the horn button would be a lot easier to replace than pulling apart the whole steering column to track down the source of this apparent current 'leak'.

I think you can honk up a storm and still sleep soundly — even if your neighbors won't.

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I had the same problem. It turns out my rag joint does not fully isolate current. It lets through enough electrons to keep the horn relay from turning the horn off but not enough to trigger the horn by itself. I am running without a horn relay and I use a circuit breaker under the dash to completely shut down my electrical system for theft reasons and battery drain through that damn rag joint.

mark

@Drumagination posted:

I had the same problem. It turns out my rag joint does not fully isolate current. It lets through enough electrons to keep the horn relay from turning the horn off but not enough to trigger the horn by itself. I am running without a horn relay and I use a circuit breaker under the dash to completely shut down my electrical system for theft reasons and battery drain through that damn rag joint.

mark

Why? If the horn is on the ignition circuit(like OE VW and Porsche) it won't be an issue.

But I guess I understand if you have it wired like a good old American car, always on.

Good point about the rag joint being slightly conductive, though. Great troubleshooting.

Long ago I discovered that my rag joint was also conductive.