horn S4

[milton]

My car came with air horns operated by a switch on the dash. I have the steering column out of the car and would like to use the original horn push to operate the horn rather than a switch. I am presuming that the return from the relay (purple/black lead) goes to earth through the steering column when the horn button is pressed. I've connected a multimeter to the end of the steering column and to the purple/black lead on the back of the steering wheel. When I press the horn the circuit is not completed. The brass terminal on the rear of the horn push does no appear to be connected to anything in side the boss. I am wondering if a part is missing from the boss. If someone could post a photo of the interior of the boss I would be most grateful. It could be that I've misunderstood the wiring.

[Pastapesto]

Hello

You need the " horn pencil" or at least that's what I know it by......all the usual suspects have them....it is basically a clear plastic tube with a brass contact at each end & to connect the brass ends/contacts there is a spring between them which allows the contacts to be in constant pressure with the brass contact on the horn push & the brass ring that fits inside the steering column that sits under the steering wheel. You will also need to make sure you have the little wire "bridge" that earths accross the steering joint at the bottom of the column & also that the steering rack has an earth connected to it.....

Hope that helps......I will now go & try to fin a diagram for you.....

A

[Pastapesto]

This is from RDents website.....I hope Ray is ok with me posting it here ......if you have not been to Ray's site it is worth a look ....he has some very interesting things on there & is a great guy.....www.rdent.com......

Not sure if this will work but if it does, the part you require is No. 17.....

[milton]

Hello

You need the " horn pencil" or at least that's what I know it by......all the usual suspects have them....it is basically a clear plastic tube with a brass contact at each end & to connect the brass ends/contacts there is a spring between them which allows the contacts to be in constant pressure with the brass contact on the horn push & the brass ring that fits inside the steering column that sits under the steering wheel. You will also need to make sure you have the little wire "bridge" that earths accross the steering joint at the bottom of the column & also that the steering rack has an earth connected to it.....

Hope that helps......I will now go & try to fin a diagram for you.....

A

Many thanks, I've ordered one from ebay.

[oldelanman]

These were used on several different vehicles, make sure you order the right one for the Elan as the lengths vary depending on the application.

[RAJ2628]

I bought a new one from from a well known supplier. I struggled for 10 mins to get the horn push on thinking I was doing something wrong. Fortunately I kept the original horn pencil and I compared it to the new one. The PO must have had the same issue and decided to cut the pencil to a smaller length.
My new pencil measured 68mm. The original was trimmed at both ends ending up at 63.5mm long.
When I put the reduced length pencil, I got the horn push to fit.
I'm not saying all horn pencils should be the short length, It's just my experience.
There shouldn't be, but there may be variances in different wheel hubs - who knows.
Sorry for the odd image placements.

[69S4]

Ah, that's probably why the replacement I bought some years ago wouldn't fit. I didn't realise there were different lengths and as my original had disintegrated I didn't have it to compare. For MOT purposes I wired the horn to a push to make dash switch, intending it would only be a temporary fix but here we still are. With those measurements I'll dig the pencil out and measure it.

[RAJ2628]

I'm not saying the 63.5mm length is correct. Even at that length I felt the horn push could still pop off. I have put that job to one side for now, but when I revisit it, I will measure from the bottom of the horn pencil recess to the underside of the horn push. It might allow me to understand the load acting on the push from the pencil. One other variable is the 3 leg spring.
Fitting a horn push should be really easy. Or is it me missing something simple.

[JonB]

No you haven’t missed anything.

When I replaced the pencil on my Plus 2, I desoldered one of the ends and shortened it from the inside so as to retain the hemispherical tip. I probably trimmed the plastic sleeve too. Quick blob of fresh solder and it was back together in no time. Horn button fitted perfectly thereafter.

[RAJ2628]

JonB, thanks, keeping the rounded feature is a good idea.
How did you decide how much to cut off.

[JonB]

It was a few years ago, but I think it was an "educated guess". I might have had the remains of the old pencil. Also, I'm pretty sure I cut the plastic sleeve down rather than the brass bits. I'm sorry, but my memory is a bit vague on this one and I don't think I wrote about it on the forum (at the time I was enthusiastically posting on all aspects of the work I was doing to the car).

However.... I have the same issue with my S4, in that I have a broken horn pencil and will need to get a new one and adapt it. I may be able to measure it for you. At the moment, my car is in pieces undergoing a nut & bolt restoration so sorting the horn out isnn't high on my list, but I'll go see if I can find the pencil.

[RAJ2628]

JonB
I am towards the last quarter of doing the same to an S4 FHC. I'm on the engine this week and doors next week. After that I'll look at this issue and let you know how I got on.
Al

[JonB]

I have found and measured the horn pencil from my S4, which I believe is original.

As you can see, it's broken, but I was able to measure it as follows:

• Sleeve (the broken bit) 45mm
• Full length 56mm
• Lengh fully compressed 48mm

Looking at your pictures, the "old" one does not look to be original.

Cheers
JonB

[RAJ2628]

JonB, thanks for that info. 8mm of compression is a good base to work from.
From your measurements it could be I need to shave off about 7mm.
That ties in somewhat with my experience that even the old cut down pencil was still putting a load on the horn push.
Why would anyone sell something that is 12mm too long.
Perhaps the distance from the bottom of the pencil counterbore to the underside of the horn push varies for different hubs. Perhaps it was an item designed by another manufacturer and Lotus used it as a "that'l do" part. Who knows.
I'll find out when I measure mine up and put it on here for others to be forewarned and dwell on.
In my first post, I did say original pencil. I meant the original one that came with the car.
I'd be curious to know what an original pencil looks like.
Looking at yours and my old one, they have both been cut down, have brass hexagon stock at either end, a spring in the middle and a clear(ish) plastic centre shroud.
All 3 of them did not fit or work as intended.
Do you have an Original Pencil Horn Spec to highlight what's wrong with all 3 of these things.
Regards Al

[JonB]

No I don't have a specification for the horn pencil fitted to the S4, sorry.

I suspect the ones sold now are for another similar car, probably a Triumph (the Elan steering column is a Spitfire part). My pencil doesn't look like it's been modified, especially the plastic part, which appears to be as moulded. I can tell because there are no rough cut or filing marks on the ends.