Bedfordman

I would welcome some comment on this: 1991 S4, In last few days my Horn has sounded at random ! Very short duration busts - a 'bp', not a 'beeeeeep'. Does not seem to be related to bumps in road, turning, speed,
I checked the wiring at the horns, under the wheel arch: looks good.
I dismantled the horn button, checked operation, all good, (I have the C18, Porsche Sport wheel).

Is there a likely place where wires may or do fray ? Guidance appreciated before dash area strip down

C18 Wheel
.
My current strategy = remove fuse.

Mrmerlin

Look at the wheel from the bottom see if the contact ring is pressing too hard on the horn tang if so then the switch should be adjusted on the column
NOTE or the tab could have been broken off if a new wheel was fitted and the switch not properly adjusted for the new wheel

dr bob

The horn contact depends on a few things, one of which is proper positioning of the switch assembly relative to the wheel hub. I use a multimeter to read the voltage through the relay coil, at the wire coming through the hub. Adjust the combo switch position to just barely contact the hub.

The top bearing in the steering column deteriorates with age and use, to the point where the horn contact on the combo switch risks damage. If your wheel can be moved up/down in the column, or you hear or feel a slight grinding when you turn the wheel, you're a candidate for a new steering shaft bearing. Replace a tired/failing bearing before you adjust the combo switch position.

jpitman2

Reminds me of a funny story. Many years ago lived in a house with the master bedroom above a car port. About 2AM one night, the horn goes off, and keeps going. Warm night, dont need much clothing so I jump out in pyjamas with torch, down to car, open hood, pull horn lead (something had shorted all by itself), and start back up the drive, to meet 2 large gents in dark suits waving a torch and a clipboard. WTF?? 'Are you no x?' one says. 'No' says I. 'Oh, OK' and off they go. Apparently 2 Policemen looking for house no x. Made my night.
jp 83 Euro S AT 57k

Bedfordman

Radio Removal Tools, bottom ends trimmed and sharpened.
Thanks for the great suggestions.
Now double checked the Horn Switch and continuity, all good.
Horn random sounding persists with Horn Switch removed from car !

Column bearing checked too. No play at all.

I am thinking the fault is the relay - although perhaps an unusual failure mode...
Ordered new relay.
Incidentally; I found that a little trimming with a hack saw of a pair of the Radio Removal Tools worked great for levering out the Relays.

dr bob

Friendly alert on using tools like that for relay removal: Disconnect the battery before using them. The rolled ends are easy bridges for relay pins. Might just honk the horn, or as easily short 30 to 31, an unfused short to ground.

Look also at the horn itself. The later brackets that hold the horns are prone to fatigue failure, allowing at least one of the horns to dangle by the wiring in the forward section of the wheelhouse area. From foggy memory, a rub-through of one of the wires risks your symptoms.

928 GT R

I had an occasional horn problem on the Outlaw GT. The problem was traced to the alarm system having an intermittent fault.

Can not help you with the fix because I deleted the alarm system and have to confess to removing the horns...

I never need to use a horn on that car because it IS a horn!

Petza914

They make relay removing pliers that work much better and don't have as much contact area under the relay to risk shorting.

There's a right tool for every job.

Does the horn only do this when the car is running, when the car is moving, or even when parked with the key out. If either of the former two it sounds like you have a wire shorted somewhere. I believe what completes the horn circuit is a the ground side of the circuit.