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MG MGA - Brake Switch Failure (yet another!)

Kind motorist following behind today pointed out I had no brake lights.
When I got home I checked it out and had power to the switch but nothing back. So it has turned up it toes!
I gather from all the previous threads that new switches tend to be rubbish. Has anyone bought one in the UK recently which has lasted any longer than two weeks? I would like to see whether there is any hope in buying a decent standard switch before trying a mechanical switch on the pedal or making up fancy electronic circuits with relays and diodes and things.

Is this switch the same as the Sprite or the MGB fitting. I believe that the Sprite contingent have tried a VW switch.

Maybe buying a quality switch is wishful thinking.
Graeme Williams

Graeme - "Maybe buying a quality switch is wishful thinking"

It may not be wishful thinking, but so far, only the Ron Francis SW 32 switch at somewhere north of $30 is the only one that has been reliable and at that, I have seen several complaints about that switch. The best way that I have found to keep the switches from failing, is to add a relay/arc suppression circuit to the switch. Adding this circuit to even the cheapest switches has proven to be reliable. See the article, Brake Light Relay in the Other Tech Articles section of my Homepage at:
Cheers - Dave
DW DuBois


The VW switch has been mentioned, but it was also pointed out that it has a metric thread.

I don't know anyone that has actually fitted one.
Dave O'Neill 2

Dave O'N: I remember there was an article in Mascot in which someone did fit it. I (lazily) haven't referred back to it yet but I sort of recall that the thread was "near enough" to be sealable with ptfe. But that is based on poor recollection of these things.

I am currently thinking along the lines of a mechanical switch with nc contacts held open (plunger depressed) by the brake pedal at rest, mounted in the footwell. At the moment having looked for a supplier, most are reticent about ratings and the Durite one which appears often is only 4 amps whereas we need to switch pretty close to the maximum and I would rather have a bit to spare!

Dave DB: I found your information in the archives. Fitting the capacitor and the solid state device seems a bit fiddly - not sure how they would be mounted?
Graeme Williams

Dave DB: I know you sell the modded relays but I now realise they are available in the uk "ready made"!
Graeme Williams

If buying a relay with built-in diode, make sure you connect it the right way, if you are still running positive earth, or you will have a dead short.

That should test the current handling capacity of your switch!
Dave O'Neill 2

If you have a few days to spare, you may wish to consult Barney's website. But answers on a postcard still very welcome.
D Smith

See here:
The ones that are tagged "Known Bad" I have personally fried in 8-weeks, 8000-miles or less. As far as I know, all of the ones made in Mexico are bad, and a few made in USA are bad. The Ron Francis switch also has a couple of reported failures, and when opened up for inspection shows similar burned contacts.

I found one made in Spain that is still good after 8-months 22,000 miles. It is Duralast RB401 purchased at Autozone, still in my car accumulating more time and miles.

I also have in my possession one Intermotor 51600 reported good by Garry Kemm, Victoria, AU (but I haven't tested it yet).

I also have in my possession one Park Remax Ltd switch PB707/ES1662 (replaces 31802/34542), made in England (many years ago). This was given to me by Bob Macherone who owns Sports Car Shop in Eugene, Oregon. This is a New Old Stock switch which Bob claims to be a good part. I haven't had the opportunity to test it yet.

See here:
This article shows what proper electrical contacts look like. Long live Lucas. Unfortunatley you can't see this in a switch until you cut it open, which destroys the switch.
Barney Gaylord

Would changing to led brake lights reduce the load across the switch and reduce arching?
d brenchley

"Would changing to led brake lights reduce the load across the switch and reduce arching?"

Perhaps, but it is an expensive way to protect the switch. Cheers - Dave
DW DuBois

Decided: going to go for the switch/relay/capacitor solution.
The issue I (we) face when buying from our usual suppliers is we have no idea who makes an item we buy, so finger's crossed and I'll try MGOC. (Ironic, eh Alan A!)
Thanks for the help everyone!
Graeme Williams

As i mentioned previously somewhere, seven years ago i fitted a bracket and mechanical switch with a relay to lower the load on the switch contacts. Works fine. Funnily enough, only a few days ago a pal of mine with an A has developed a sluggish switch so that the lights only come on if you really lean on the pedal - sounds like another candidate for a mechanical replacement.

Colin Manley


I had the same issue as your Pal, also about 7 years ago, but a new switch from Bob West has served me well since.

Amusingly, the issue was brought to my attention by a police car that was following me up to traffic lights. When stationary waiting for green he informed me over his loudspeaker that my brake lights were not working. I turned round in my seat to look at him, more in surprise than anything, pushed hard on the pedal to illuminate the lights. Nothing more was said until we moved off, when he then said over his loudspeaker: " Nice car".

Steve Gyles

It's worrying from the point of view that although "one should" one doesn't really very often check the brake lights are working. When it was pointed out to me i felt very conscious about it and tried to avoid braking! They make have failed weeks ago!

Can anyone tell me this:

The switched signal from the sensor switch must join the feed to the rear of the car. I would like to find that connection. I would guess it will be somewhere round the steering column area. Can anyone be more specific please?
Graeme Williams

Graeme - "The switched signal from the sensor switch must join the feed to the rear of the car."

It goes back on the green/purple wire.

" When it was pointed out to me i felt very conscious about it and tried to avoid braking!"

A better way would be to add a wire to the output of the switch (or the relay) and run it to a convenient spot on the dash where you can install a tattle tale light that will come on every time you step on the brake. Cheers - Dave
DW DuBois

Thanks Dave but I was wondering if there was a bullet joint handy as it would be a good place for the relay. Just hoping someone could tell me where to look. The capacitor - is it polarity sensitive? I know the relay will be.
Graeme Williams

The bullet is just underneath the starter switch inside the engine compartment.

Don't fit a relay, just reduce the load on the switch by fitting (red) LED bulbs at the rear.
dominic clancy

Thanks Dominic. I would have been looking in the cockpit.
THe relay is about 3.50, and the capacitor about 40p so if it saves the switch it isn't an expensive solution.
Graeme Williams

You can use a VW switch with an adaptor. Dr J.E.Davis brought all the parts to the last meet. He is coming on our next Old Boys run so you could come and see the parts and discuss it with him.
Alan Anstead

Alan: I wasn't sure whether the fitting was the same for both Sprite and MGA. I have decided to fit a standard MGA unit (from the MGOC!) with spark supression and ordered the bits this morning. Obviously the car is off the road until that's done and I have an mot due in te next couple of weeks.
Graeme Williams

I could have made you a custom fitting if need arise on my lathe.
Alan Anstead

A mechanical switch is an easy fix if you get frustrated trying to find a high quality switch. Can be done for about $A30. Also is more sensitive to pedal touch. See sample set up below
Mike Ellsmore

I have found that the switches supplied by Harley Davidson as replacement parts are good in both silicone and conventional fluid systems in my MG's.

And Yes, the threaded fitting is british on a Harley Brake Light Switch !.

They still fail after around 5 years, but not using the cars every month is likely not helping ?.


Black Mountain

My Harley switched failed in 8000 miles, same as a bunch of others. Have a few more reports of failed Harley switches. No better than the ones made in Mexico. The threaded fitting is 1/8-NPT (American or British post war).
Barney Gaylord

Update: despite having bought the hydraulic switch I have abandoned that solution. Several here have said that there is a risk of tearing out the hydraulic connections if the fitting turns and I found that I couldn't get good enough access to hold the fitting and turn the switch. Access is pretty poor and the switch seemed very tight. If I had been doing the rebuild I would probably fitted the switch on the bench and therefore it may well be tight to remove "on the car".
Today I made up a bracket and fitted a plunger-activated switch on the brake pedal. Having got the parts, I will still use a relay and the spark supression to increase the switch life (I guess that is still desirable).
Graeme Williams

The 3rd brake light in my '34 'rod is inside the rear window, so I always get a reassuring glow in the mirror.

I had wondered about putting a tell-tale light directly off the switch down in the foot well. Perhaps that's getting a bit neurotic.
Graeme Williams

I wouldn't put a tell tale light there, it will distract you just when you least want distraction.

I have a high level brake light that sits on the tonnea studs: when I first back the car out of the garage, I just glance at that for working proof.

Colin Manley

Thanks for that advice Colin. I will forget the idea of the tell-tale in the footwell.
Graeme Williams

All done:
Bracket made
Bracket modified
Bracket fitted(!)
Wiring modified.
.. and it works just fine

(Bracket courtesy of of Ikea. A few years ago they produced stacks of square jotting pads set in an ally container. That has made two switch brackets and the brake light switch bracket.)

Graeme Williams

FWIW I replaced a dud brake light switch on mine with an Intermotor version bought off the shelf in a local auto spares shop, mainly dealing in just modern car stuff, and to my pleasant surprise it was correct thread, screwed straight in and has worked fine for around seven years now. And that's with standard 21watt old style stop lights, ie. no relay, and silicone brake fluid. (Not that silicone has any influence on this issue anyway, but also conscious of not wanting to rekindle that myth again!)
Thought Barney and others might be interested in my experience for the record.
Bruce Mayo

I guess the problem is that these companies buy in bulk batches from whoever quotes the best price. Intermotor then may not be as good now.

Anyway, it's fun jammed down the footwell with one arm pinned to your side trying to undo a bolt for which you really ought to use the other hand if only you could get it up the tunnel at the same time (and retrieve the spanner).
Graeme Williams

For Dominic Clancy,
In your post you suggested that one can reduce the load on the brake switch by using led bulbs in the rear lamps. Will led bulbs work on a positive earth wiring system?

F. Camilleri

Frank, you can get both po and neg led lights, fitted all our old cars and work fine.
d brenchley

This thread was discussed between 06/03/2016 and 18/03/2016

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