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MG Midget and Sprite Technical - non-working hornire

Well, its quiet on the BBS - I think folk are getting bored with Prop's sagas, so here's another conundrum.

1971 Sprite, and the horns don't work. Well, not exactly true, the horns do work when tested on a battery. They also work when plugged into their purple (permanent live feed wire)but only if I add a connecting wire from the purple/ black wire at the horns and touch it to earth.

But they don't work from the horn push. And as this is a known weak point I tried making an earth connection from the purple / black wire where it exits the main loom to the multiplug that supplies the steering column stalk switch. Still nothing. This suggests to me that there is a break in the purple/black wire on its route through the loom. But the complete loom was replaced a few years ago and is in good condition, so are there any extra connectors between scuttle and the horns that might have come loose? Or any other suggestions.

Actually I never bother much with the horns as, not being Italian,I never use them. But the MOT is due!

And the edit option doesn't include correcting the title!
Guy Weller

If horns and wipers aren't used or tested fairly regularly they can stop working especially in summer

Guy which/where is your horn switch?

Have you got a copper ring?

How long have you owned the car?

check/clean all connections (there are no connectors)

disconnect battery and clean fuse and fuse connector spring clips, connections to fusebox (and fuse) horns are power hungry and want full meal
Nigel Atkins

Thanks Nigel,

The horns work fine when supplied by the normal wire through the loom, with the circuit momentarily completed by an earthing wire from the second horn terminal direct to the bodywork. So from this I presume that the supply side - battery, fuse, connectors etc is all OK.

The horn switch is on the end of the indicator stalk, so doesn't use the copper ring and pencil arrangement. But anyway to eliminate the switch installation I was trying the same test again with an earthing wire from the purple/ black feed at the multiplug to the column switch. But this time - no sound! It suggests a break in the earth return wire so I wondered if there was a connector somewhere that had come loose.

I have owned the car since 1989. It usually gets driven every day except recently when it has been off the road for a few weeks respray and some other renovations. Its about ready for a re-launch, commencing with an MOT, but for this the horns do need to work!


Guy Weller

stalk to loom is the only connector apart from spades

I had trouble with my horns, only one working but both worked fine when connected directly to battey individually

In the end it was a corroded connection at one of the spades one of the horns

If I've read it correctly you've taken a wire from loom connector Pb direct to an earth point which would complete the curcuit and sound the horns if the earth contact was and the loom connector contact were both good

As my car came with a DIY horns switch and you say it's a known weak spot it still suggests maybe your switch or loom connector rather than loom

I'd still check the Pb spade connectors are clean and tight fitting on the horns

To eliminate the loom and loom side of connector you could run a wire from stalk side of connector to Pb connector on first horn using a fresh new spade on this which also has a second piece of wire coming out of this spade to another fresh new spade to connect to the second horn at the same time

If horns don't work with above then it's stalk side, either switch or the wire or loom connector

Hope that makes sense

By the way mine passed the MOT with only one horn sounding and that was so weak you couldn't hear it sitting in the car
Nigel Atkins

Yes that makes sense.
The test at the horn end of the loom was by connecting one horn to the loom - both the permanent live purple and he earth Pb. And then jumping the Pb for the second horn connector direct to an earth point. This tested the operating horn, the spade terminals to it and the live feed. All OK.

As the second test skipped the horn switch itself out of the circuit the only difference should be that I make the earthing connection from the dashboard end of the same Pb wire. If there aren't any hidden connectors it suggests a break in the wire somewhere in the loom. The loom itself was new some years ago and a good quality one but it might have chafed through somewhere obscure!

I only use one horn anyway. It is an ex-scrap yard one from a Citroen XM, designed for French motorways and Paris so is very loud!

Guy Weller

The horn circuit on the early cars is very simple, the route is as follows:

battery -> horn -> horn switch -> earth (battery)

The problems are usually all with the earth connection. First, the switch must make a good earth contact (via the copper ring) to the metal steering column. THEN the steering column must make a good earth contact to the body of the car - and this is where things usually go wrong. Open the bonnet & expose a small bit of bare metal on the steering column. Then, with a test meter or test bulb or similar, make sure that there is NO resistance between the column and body/battery earth. The usual way to ensure this to attach one end of a short earth wire to one of the aluminium brackets which secure the steering rack to the car - and then attach the other end to a good earth on the car. To test if this is your problem, try attaching a jumper cable from bare metal on the steering column to battery earth. If the horn does not spring to life, your problem is probably a poor earth at the switch. Be VERY careful attaching any earth wire to one of the purple wires at the horn because choosing the wrong terminal will short circuit the battery & blow the horn fuse!
J.E. Davies

Lot simpler with one horn as I think (maybe, possibly but not sure) sometimes two have to work together, wired in series parrel - oh I don't know, schooling was many many years ago for me

Part of my problemwas the guy who put in my dash toggle horn switch used a 5 amp which wasn't man enough for the job

For safety sake I ended up replacing not only the spade connectors but also the momentary (sprung) toggle switch for a heavy duty and 25 amp but also both horns for cheap aftermarket ones

It now sounds more like a truck than a midget but it will now warn rather than just amuse

ETA: JE - he's not got a copper ring
Nigel Atkins

Just remembered

I also fixed the new horns underneath the supporting brackets out of the (direct?) airflow to the rad

the old horns were fitted on top of the brackets sitting in view thro' the rad grille
Nigel Atkins


1) Twin tone horns are connected in parallel and do not complicate this discussion.

2) All steering wheels with a centre horn push must have something like the early copper ring and connecting pencil. Midgets Mk2 and 3 have a 'Slip-ring' and connecting pencil (parts BHA_5042 and BHA_5041).

3) x1 correction (sorry) - one end of the small earthing wire should be connected to one of the steering rack bracket's set screws, THE OTHER END SHOULD CONNECT TO ONE OF THE SCREWS SECURING THE RACK'S PINION COVER. This should ensure a good connection between the steering column and chassis earth. This little wire is often forgotten (omitted) during restorations. I've attached a photo which I hope makes the connection clear. OK?

J.E. Davies

I agree, one horn or two makes no difference to how they work - or don't!

Mine is a '71 car. It uses a column stalk switch which is independent of any earthing through the steering column as it has an earth lead direct to the switch, not via the column. Even so, my testing has been by completing the circuit to earth rather than relying on the switch to earth. Still not sussed it out though!

Guy Weller

Sorry Guy, I've rarely read past page 73 in Terry's book, I don't know much about the later cars, I never knew that some of the Sprite IV and Midget III facelift cars had a horn control on a stalk! My comments apply only to horns operated with a centre steering boss. Your problem (whatever it is - the switch?) might have happened quite a lot because I see (reading page 116) that horn control returned to the centre boss at GAN5-89515 and HAN10-86303. Good luck with your attempts to fix it.
J.E. Davies

My Triumph had a bridging wire to make the horn work and sometimes after the car had been jack up as the car settled the horn would sound

Guy have you eliminated the switch and stalk to loom connectors yet or are those still to be tested?

The horn arrangement on these car (especialy yours with only one) may be straight foward but I'm sure (might be wrong of course) that this is not always the case
Nigel Atkins

Guy, I believe that this circuit diagram is the one for your car ...

Well your horn anyway, because this arrangement (horn switch integral with the stalk) existed for only a very short time - all other diagrams have what looks to be a very much more robust separate horn switch with its own earth connection (this website contains diagrams for all Spridget models).

If your horn switch is faulty, then joining the two wires which serve the horn switch (one purple/black, one black) should make the horn sound. With this diagram, it should be easy to find the fault. Good luck & thanks (I've learnt something extra here about the history of the horn circuits).
J.E. Davies

Nothing to do with the horn push-switch - I knew it wasn't as I had by-passed the switch itself right at the start as I know they can be suspect.

Turned out to be the return earthing wire (Pb) inside the loom had broken (fused?) just inside the front slam panel. I tracked it down by sticking dressmakers pins into the Pb wire at various points along its length and checking for continuity with a meter. The pin trick is a bit of a last resort but works surprisingly easily. Once I started with that it was very quick to narrow down the break.

Thanks for the wiring diagram, JE. Useful for another occasion!

Guy Weller

well done

you were right and you persisted

a bit of something applied with a pin will fill in the pin ho;es
Nigel Atkins

Nigel, there aren't many pin holes. First one about half way determined which half the fault was in. Then halved that, and again. Then guessed it was where the harness bent around a corner and - Hey Presto! I touched a little super-glue into the pin holes but it was probably not necessary, they pretty well closed up as I pulled the pins out.

Its a neat trick though. I have used it in the past and then forgotten about it until today when the idea re-surfaced unexpectedly!

Guy Weller

Good trick I've not heard of it before

My mate had a bit of kit that could detect the lenghth to the end or break in wire but couldn't work out how to use it (used for commercial/industrial installations)
Nigel Atkins

I'm glad you found the fault Guy, how did you fix the break? Strictly, the purple/black wire is not an 'earth' wire because the purple and purple/black horn wires are always 'live', a dangerous arrangement that would probably be illegal today - but it was the simplest (cheapest!) way of making the horn work IF THE HORN BUTTON IS IN THE MIDDLE OF THE STEERING WHEEL. This danger was recognised in the early cars which had one fuse for the horns and another for everything else. It's interesting to note that this dangerous mode could have been eliminated (I think) with your horn-push-on-a-stalk by simply reversing the direction of the supply - a single live wire could go straight to one side of the switch and the earth could be at the horn end. This would save wire (only one wire need go to the horns) and be much safer (because there would be only one very short length of live wire between switch and battery). Why this was not done is a mystery, I cannot explain it - but then many mysterious and logic-defying things happened within the company as time went on. One further query - is your loom original or a modern replacement? The original LUCAS looms had great big thick 17 strand copper wires for the horn & main-light circuits which perforce must carry large currents. Today, the price of copper means that some modern replacement looms are rubbish: they have thin non-copper wires which might be better fuses than the fuses in the fuse box ...
J.E. Davies

The loom is a replacement, bought maybe 15 years ago by me. But it is a good quality one. The Horn and light circuit wires are noticeably thicker than the others. I could check the gauge / number of copper strands but I think they match the original spec. My light circuits are re-done with relays so the current running through those little contacts in the switches is much reduced.

You are right about the wiring arrangement. Very odd and difficult to come up with any sort of a logical explanation.

Oh, I fuxed the break with a crimp connector. I was going to solder but the problem is then that solder runs down the wire and the cable looses its flexibility. I think the crimped connector inside a heat-shrink sleeve is better.
Guy Weller

Thanks for the thread, folks, and glad you fixed it Guy. You have the patience I lack, but have inspired me to fix my elusive horn fault this weekend.

My last two MOTs have been obtained thus.......


Andy Pie-Crust

Andy, that's brilliant! I like your style!
Guy Weller

Andy is obviously a person who never lets a practical problem beat him. Is he an Australian? Guy, I agree that crimping is a good solution - another way to do it is simply to ignore the old wire, run a brand new one and tie it to the loom with cable ties - with a little attention to detail, it would have to be a very eagle eyed concours judge to spot it ...
J.E. Davies

JE, Concours - hardly!
But I don't like extra wires tied to the loom with cable ties. If I do add a wire it has to be wrapped in with the others. I am quite happy unwrapping lengths of the loom and re-doing them to include an extra wire if needed. But then not being into concours I don't use that pretty herringbone cotton loom wrapping. Its plastic, self annealing tape and corrugated split plastic tubing for me!
Guy Weller

This thread was discussed between 30/08/2010 and 02/09/2010

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