Intermittent horn problem - help!

[tim hunt]

My 4A has developed an irritating fault, the horn operation having become hit and miss. I know this is a common complaint but I have never previously had the problem. Strangely, the horn button consistently fails to operate the horns when the wheel is roughly between the straight ahead and 2 o'clock positions. For the remaining 300 degrees of rotation the horns operate normally with the button. I removed the horn push and on pressing it I found low resistance between the brush contact and the spring on the side of the push that earths to the Motolita steering wheel bush. I jacked the front wheels clear of the floor and carefully shorted the horn contact brush to earth as I turned the wheel. Again I found no horn operation between 12 and 2 o'clock  but that the horn worked perfectly with the wheel in any other position, exactly as I find when driving the car. It occurred to me that possibly a segment of the slip ring contact might be damaged or missing but on removing the steering wheel I found this contact to be in perfect condition. Indeed, if I short this contact to earth all round its circumference the horns work at whatever position I earth the slip ring. 

I have a functioning air horn so am able to give audible warning of approach. However, this is fine and dandy on the open road but I do not want to scare the errant pedestrian around town and need the normal horns working perfectly on the odd occasion they might be required. Any bright ideas?

Tim

[TR NIALL]

6 minutes ago, tim hunt said:

My 4A has developed an irritating fault, the horn operation having become hit and miss. I know this is a common complaint but I have never previously had the problem. Strangely, the horn button consistently fails to operate the horns when the wheel is roughly between the straight ahead and 2 o'clock positions. For the remaining 300 degrees of rotation the horns operate normally with the button. I removed the horn push and on pressing it I found low resistance between the brush contact and the spring on the side of the push that earths to the Motolita steering wheel bush. I jacked the front wheels clear of the floor and carefully shorted the horn contact brush to earth as I turned the wheel. Again I found no horn operation between 12 and 2 o'clock  but that the horn worked perfectly with the wheel in any other position, exactly as I find when driving the car. It occurred to me that possibly a segment of the slip ring contact might be damaged or missing but on removing the steering wheel I found this contact to be in perfect condition. Indeed, if I short this contact to earth all round its circumference the horns work at whatever position I earth the slip ring. 

I have a functioning air horn so am able to give audible warning of approach. However, this is fine and dandy on the open road but I do not want to scare the errant pedestrian around town and need the normal horns working perfectly on the odd occasion they might be required. Any bright ideas?

Tim

Wire them direct to a push switch maybe if the fault can’t be found.

[RogerH]

Hi Tim,

Have you got the steering box earthed.  I have a separate wire at the bottom end to ensure earthing stays complete.

 

Roger

 

[john.r.davies]

Tim,

Triumph wired the horns so that they are live, permanently 12V+.     They sound when they are earthed, which of course can be anywhere on the car.    The steering wheel boss is part of the normal earthing circuit, which should find earth through the steering column when you press the horn button.    But if the boss touches the shroud around the column, then this will also complete the circuit, and - HONK!    Inspect the column and shroud, and see if they can touch anywhere while turning the wheel.

JOhn

[Richard B 2.5PI]

Tim,

Have you got an earth wire on the steering column U/J's connecting each side of the U/J?

[tim hunt]

10 hours ago, Richard B 2.5PI said:

Tim,

Have you got an earth wire on the steering column U/J's connecting each side of the U/J?

Yes and in answer to Roger I also have a supplementary sprung contact permanently earthing the lower steering column to the body, see pic. As for John's input the horn never operates inadvertently, my problem is as described, the horn push only operates the horn through approx 300 degrees of steering wheel rotation. Thanks all.

[stuart]

1 hour ago, tim hunt said:

Yes and in answer to Roger I also have a supplementary sprung contact permanently earthing the lower steering column to the body, see pic. As for John's input the horn never operates inadvertently, my problem is as described, the horn push only operates the horn through approx 300 degrees of steering wheel rotation. Thanks all.

Have you checked that you have continuity for 360 degrees, it maybe you have a short horn pencil and if the steering wheel hub casting is slightly out of concentric it’s not actually contacting for the missing period 

Stuart

[john.r.davies]

13 hours ago, tim hunt said:

Yes and in answer to Roger I also have a supplementary sprung contact permanently earthing the lower steering column to the body, see pic. As for John's input the horn never operates inadvertently, my problem is as described, the horn push only operates the horn through approx 300 degrees of steering wheel rotation. Thanks all.

Ah! My mistake.   Then suggest removing the steering wheel and applying engineers blue, or a felt tip, to the contact strip.   After reassembly, testing by turning the wheel and then dissemble again.  You will see if the 'pencil' is contacting the strip all round.    If not, then  there is some distortion in the whole assembly.     If it does make 360 contact, then the problem is elsewhere.

John

[tim hunt]

Thanks Stuart and John, good suggestion. I'll try that and report back.

Tim

[MKTR]

Hi Tim, 

I had a similar issue a few years ago and it turned out to be the 'pencil', which was loose in the boss and would sit at an odd angle when the steering wheel was at 12 o'clock. Turning the steering wheel a bit just moved the pencil connector away from the ring.  Solved with some tape around the plastic casing to force it to sit better.

Mark

[tim hunt]

On 4/17/2025 at 11:56 AM, MKTR said:

Hi Tim, 

I had a similar issue a few years ago and it turned out to be the 'pencil', which was loose in the boss and would sit at an odd angle when the steering wheel was at 12 o'clock. Turning the steering wheel a bit just moved the pencil connector away from the ring.  Solved with some tape around the plastic casing to force it to sit better.

Mark

Thanks very much Mark, sounds like you could be on the money. I will try your suggestion today. After all, from all my tests to date I have concluded the issue must be related to the brush 'pencil' in some way.

Tim

[tim hunt]

I just tried some tape on the pencil, it didn't need much to make it a really snug, just sliding, fit in the boss. Disappointingly my problem remained, no horn with the steering wheel between about 12 and 2 o'clock. I wondered whether it might be an earthing problem after all and connected my multi-meter between the top of the upper steering column and a good earth. With the front wheels jacked clear of the ground I then turned the wheel to and fro.  Lo and behold I found continuity for most of the rotation but no resistance with the wheel between 12 and 2. More investigation to follow tomorrow -I won't be beaten!

Tim