924Board.org

[coup85]

My horn won't work. I can hear the relay of the horn 'activating' from the panel when I press the horn button at the steering wheel but without the horn sounding.

As I think is kind of usual, it doesn't activate 100% of the time as the connections aren't at their prime, as with other units I heard from, it mostly works –activates the relay– when the steering wheel is straight. But again, the horn doesn't work.

I used a multimeter to read the cables at the horn and only got around 0.2V when pressing the horn.

I also used a new horn –tested directly at the battery to be sure is ok– and it doesn't work either when connected.

I also tested the relay with a tester and it's fine –indeed is new–.

The thing is, I really don't know what to do next because I never worked any wiring in the car apart from some minor fixes. If the solution is to rewire the horn from the fuse panel how and where –the hell– I start?
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924 - 79'

[924RACR]

Hmmm, yeah sounds like maybe you have multiple problems to work through here.

For one, you say that the horn relay will click if you hit the horn button when the wheel is straight - but only when it is? This makes me think maybe you have an issue with the contact in the steering wheel hub - which would want removal of the steering wheel to inspect, maybe clean, make sure you have good contact all the way around.

If you can reliably get the relay to actuate, that means you have a working horn switch and relay ground... then you need to look and see if you have power at/through the relay for the horns (the other circuit). I'm guessing you probably don't.

I don't have the circuit diagram for exactly your car, but it's unlikely it's changed any much across the years. From what I do see, the relay should always have power at the #30 terminal (hot wire directly to battery). So you should be able to, with your voltmeter, find +12V or so (battery voltage) at the #30 terminal on the relay (markings are on the relay face, from what I remember).

Furthermore, if you then jump this with a free piece of wire across to the opposite terminal on the relay board - should be #87 - that should send power/+12V to the next item in the chain.

Which is the fuse - looks like #1 on the additional fuse board.

You did check the fuse, right?

Note that all these checks do not require ignition power.

So if you jump those terminals on the relay board (and assuming you have 12V at #30 at the relay), then you should have 12V at the fuse.

After that, it should be a direct wire, with only a couple of connectors, down to the horns themselves.

Maybe check these then reply back?
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[coup85]

Thank you, I’ll proceed to check and revert.
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924 - 79'

[Raize]

The horn location is very exposed, sometimes it can just be that the connectors have become horribly corroded and can no longer conduct electricity.

I have never had a consistently working horn but to be honest it helps prevent road rage incidents anyway.

[coup85]

Update 1: I restored the power back to the horn but still having problems with the grounding.

Now, with the steering wheel off, the horn only works when you close the circuit over the metallic plate on the center of the steering wheel, not on the axis, which I think is supposed to ground the horn when you press the button on the steering wheel.

Picture –this way the horn sounds–:

https://i.imgur.com/vgeD77e.png

Video: https://imgur.com/SqWSy65

The resistance measure with the multimeter on the center of the column is 1.0.

I tried to look for the grounding of the steering wheel column, but I couldn't find it.

Also cleaned the connection of the steering wheel –the inner metallic circle– that had some kind of grease on it.
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924 - 79'

[coup85]

PS: I could use a temporal solution as I need the horn to pass the technical inspection to be able to drive the car.
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924 - 79'

[Raize]

It's meant to ground through the steering shaft, it's not very clever because the grease in the steering shaft bearings obviously doesn't let it conduct.

What I did back when I still needed to pass technical inspection was to sand away some of the paint on the steering shaft lower down and I used a jubilee clip to attach a wire to the bare metal with the other end of the wire grounded to the body and enough length of wire to be able to "wrap" around the steering shaft as it turned. It will still break eventually though (well, mine did anyway - maybe if you use some good cable it can survive).

[coup85]

I’m definitely trying this at least as a temporal fix. Thank you!
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924 - 79'

[coup85]

Final update: The problem has been temporarily resolved. This information may be useful for anyone who encounters a similar issue. Apart from the previously mentioned.

1. Cleaned the connections of the back relay panel -the one for the horn is the A connector- and changed the fuse or the aux panel (#1).

2. Rewire the grounding of the column following @Raize instructions. Kind of easy, just be sure to leave enough cable for the column to steer and try to use two hose clamps to secure the cable on the column.

3. I finally installed new horns as the old ones were pretty damaged and remade part of the wiring -the part accessible from the front wheel-.
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924 - 79'