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MG MGB Technical - Horn Problems

I took my 76 roadster for a MOT yesterday and also had new tyres fitted. Although a MOT is not required for the car, I like to get it tested for peace of mind that it is roadworthy.

When I picked the car up the mechanic said all ok and it has passed, but there was one problem - "when we turn the steering wheel the horn goes off"? I had a quick look and disconnected the horns. When I got home I found one blown fuse and when I took the horn push off the steering wheel I found one of the horn slip ring securing screws loose. Taking the cowling off, I found that the slip ring had slipped one side and had obviously been earthing out when the wheel was turned.

I've had the car for ten years now and although the steering wheel has been off to replace the ignition switch, I've never touched the horn slip ring, so I assume it's original. You can see from the photos that one of the fixing lugs had broken and the other is cracked and about to break, I'm assuming because of age.

It was fine taking the car to be tested and it just goes to prove sods and murphy's law and what those pesky little gremlins will do........

Andy






Andy Robinson

If you haven't got one already they are available from the usual suspects - BHA5042.

But that shouldn't have blown the fuse (the bottom one) to the purple circuit, in fact if the horns were sounding it hadn't blown, and if hadn't been sounding it would have failed the test. Which fuse had blown?


paulh4

Thanks Paul, I've ordered a replacement from MGOC.

It was the bottom Brown/Purple fuse that had blown. Looking at the wiring diagram the horn could have picked up another battery supply via the headlight switch and headlight flasher, but it's unlikely that both of them are faulty. I have an alarm fitted to the car and I think it's more likely that could be the cause. It's difficult to say what was going on inside the steering wheel boss, with the slip ring assembly floating about and whether that could have picked up a battery supply.

So it's out with the multimeter and 81's tomorrow to see if I can track down the cause. My money at the moment is on the alarm.

Andy
Andy Robinson

Purple goes direct from the fusebox to the horns before 1977 - if you have 2-terminal horns, but sources vary as to exactly when the change to 1-terminal horns was as they had 12v going via the horn push.

More likely to be the headlamp flasher if 2-terminal if something was floating around near the flasher contacts, or courtesy/boot lights, and I think the wiring for the GT HRW was in the main harness even though it wasn't used on the roadster of course.
paulh4

Thanks Paul. I've checked out the car alarm, which is only a simple one that detects voltage change when the doors are opened and movement - all seems ok. This has it's own siren and does not use the horns (forgot that!).

You can see from the photo of the slip ring that there is some scoring/scratching on it and it looks like it could have picked up a battery feed from the flasher/indicator switch on the blue wire (thanks for the photo from your website by the way). So I'm assuming that is why the horn was going off when the wheel was turned. As far as the fuse blowing, what I think happened is that when I quickly disconnected the purple wires from the drivers side horn, it shorted out on the body of the horn and blew the fuse.

Just waiting now for the replacement slip ring to put it all back together. The biggest bind with this job is having to take the steering wheel off and drop the the column down to get the cowling off.

Andy






Andy Robinson

The slip ring would have to pick up an earth to sound the horn, and if contact with the indicators circuit had blown a fuse it would be the second one up for all the fused ignition circuits.

So the horn sounding has a reason, but the fuse blowing not ... yet :o) However if you rarely use the horn it could simply be that the fuse was on its last legs and the flurry of activity tipped it over the edge. I assume it was the standard 17 amp rated, 35 amp blow.
paulh4

I finally received my replacement horn slip ring yesterday. There has a lot been said on this forum about rubbish parts and here is a great example.
Spot the difference between the old and the new part - there is no hole in the replacement part to fit the horn brush through onto the slip ring!

Obviously wherever this thing was made they were unable to produce like for like! The part is now winging it back to MGOC Spares for a refund.

Andy





Andy Robinson

Sundry other place do show the hole, but whether it's in current stock is another matter. Not that one should have to, but under the circumstances you may end up needing to drill your own - carefully!
paulh4

I had just posted that on their parts website they don't show photos but do when selling on ebay.

I'd be tempted to look for a s/h one and just clean it up.
Nigel Atkins

Thanks Nigel. I've emailed MGOC and complained and sent the part back to them. I've ordered another from AES and their website shows the part with a brush hole, so hopefully that one will be ok. If not, then I'll look for a second hand one.

Andy
Andy Robinson

Funnily enough their one on ebay shows a hole so probably a batch fault, or change of supply/supplier. Probably works out less cost to put up with such as this at the trade bulk price of the item.

https://www.ebay.co.uk/itm/254406235970

If you get stuck I've a mate that's supposed to be sorting parts to clear.




Nigel Atkins

Even when you get one with a hole for the pencil that connects the back of the slip-ring to the horn push you may find that the screw holes are not tapped. I've not found screws for this listed anywhere but both mine use screws with a course thread so I suspect are self-tappers. Anyone who didn't have the original screws would need to be careful using replacements, or tapping the holes, to avoid fractures.

Incidentally although it's called that in the Parts Catalogue but 'pencil' elsewhere what goes through that hole is not a brush. It doesn't rub on anything, unlike the column-mounted brush that rubs on the other side of the slip-ring as the wheel is turned. It's just a sprung contact, and rather over-engineered for what is actually needed. Moto-Lita wheels just have a wire soldered to the back of the sip ring going to a stud on the back of the horn-push for example. When replacing one of those with an original wheel rather than 'spring' for a new pencil I just used a wire. How often do you remove the horn push let alone walk off with it in your pocket?
paulh4

I sent the original replacement slip ring back and received another from a different supplier and it has the same problem, with no hole for the brush pencil! I have removed the brass slip rings from both the plastic bodies an lo and behold, there is a hole for the pencil, but in totally the wrong place!

The top picture is the new slip ring body and the bottom is the old one. The hole in the new one is 180 degrees out of phase and is covered by the brass ring when fitted and is not drilled where the flanges can hold the pencil in the correct position. Next step is to drill a hole in the correct position using the old one a template.

Beware rubbish parts!

Andy





Andy Robinson

You have to laugh ...

But if you cut the tab that's covering the hole back just far enough to clear it, won't the pencil then go through the hole to the back of the slip-ring as it should?

The two 'cheeks' are closer together that side than where the hole should be, but the longer springy bit of the pencil should go at that end and not the shorter fixed piece, so that might not matter.

paulh4

Andy,
you've now found that many retail suppliers get their parts from the same trade supplier, I might be wrong but a lot of the smaller suppliers seem to buy from Moss, and perhaps even the bigger suppliers, as the parts have the same quality and/or errors.

I've seen MGOC have some parts made for themselves but it's not many.

It's why sometimes a s/h or refurb or repair is better than buying a new modern made replacement part.

I suppose we should be grateful we can still get the parts, even if we have to modify them ourselves, as long as they work reliably for a reasonable time.

At the retail purchase price you would hope to expect more but I expect it'd need to double to guarantee this and as I often put tight-fisted classic vehicle owners wouldn't pay the extra as they helped with the rush to the bottom with wanting everything to be cheap so that is what the rest of us have to put up with, cheap.
Nigel Atkins

Success - it's fixed. I drilled a couple of pilot holes through the old slip ring mounting lugs and screwed it onto the new one. I used the old slip ring pencil hole as a template and then drilled the brush pencil hole in the right place in the new one.

Obviously you really shouldn't have to go to all this bother when you are buying new parts, but as I couldn't find any NOS or second hand parts, I had little choice.

I'm not sure how these slip rings are made and whether they are injection moulded or laser printed, but it seems funny that the hole for the pencil is exactly 180 degrees out from where it should be and is a mirror image. Computer aided design maybe?

Andy
Andy Robinson

Andy,
well done.

I might be wrong but I feel you might be doing as some do towards the cars and that is crediting far too much manufacture/engineering sophistication to them.

I may well be wrong but I imagine a lot of manual labour to manufacture, assembly and finish to a lot of parts.

It could be as simple as having the plastic the wrong way up for drilling, I doubt if drawings and samples are ever seen by those doing the work.

If you've ever seen the working conditions of some factories in this country you can imagine how much worse they might be in other parts of the world.

Remember the reason Leicester was in local lockdown for so long.

I do admire your optimism and wish I still had good stocks of it but the retention levels are somewhat lower now.
Nigel Atkins

Surely it would have been injection moulded, not drilled at the manufacturer, but it's irrelevant anyway.
paulh4

Then the mould has the hole in the wrong place and they'll all be wrong.

If the hole is forgotten then it'd need drilling out.

Again, just because it's a part for a MG you're possibly giving it and its production a level of sophistication above what it deserves and actually happens, and this isn't the 1960s this is after the race to the bottom of price and quality for classic car parts, and many other items.
Nigel Atkins

The hole is in the wrong place, not forgotten, so a moulding issue as I can't see them being drilled after moulding.
paulh4

You are most probably right and I like your certainty but I wouldn't want you on a jury. It depends where they're made as to how they're made. How on earth could they get the moulding wrong then, it's simple enough to copy - but they did get it wrong what sort of manufacturing stringency does that suggest to you. Sometimes it's cheaper and easier to correct these things by hand, labour is so cheap in some places, particularly if it's forced labour, and even when it's not.

A mate resisted as long he could but eventually had products made in China and it was less cost to pay his workers in England to correct the involved mistakes made the Chinese by paying his UK staff to correct them by hand than return or recycle the product and these were very low price items, that's how much cheaper it was to have the products made in China, and put up with the errors. The items were bulk sold valued in pence not pounds each.

And don't think they aren't sweatshops all over England and not just with the likes of Boohoo.

I'm sure we'll never hear of this problem again, all stock will be withdrawn and replaced by the correct stock.
Nigel Atkins

Last paragraph - ho ho!
paulh4

One can dream!
Nigel Atkins

This thread was discussed between 07/05/2021 and 16/05/2021

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