MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Stop light switch

Brass switch in the brake hydraulic line seems to be u/s. No stop light when brake pedal depressed, bridge the wires at the stop light switch - and hey presto....

Options therefore

Clean it out and try again - what's inside just out of interest? Any seals/O rings?

Buy a new one

Junk it and retrofit a simple spring loaded mechanical one.

Obliged as always

Mark
Mark O

Mark,
The originals are far better made than the replacement versions, so try this first. Slacken the switch by maybe 1/2 a turn and pump the brake pedal to force some fluid out past the threads to clear any air bubbles. Retighten. Sometimes works. Best if you use the Attractive Assistant (check in your boot)

If this doesn't work it probably needs a new switch. The problem with these is that the contacts burn out with the current flow, usually within 2 years! A good "upgrade" is to add in a relay so that the switch doesn't handle the full lighting current and it will then last much longer.

The old switch isn't designed to be dismantled, but there's no harm in some experimentation!
Guy Weller

Many thanks Guy - appreciated...I replaced the brake fluid wholesale not so long ago - previous PO put in the green Citroen hydrualic fluid and wrecked the seals - don't ask....too painful... hence my questions about the internals.I forgot about the switch, so yes, bleeding it seems a sound idea....
Mark O

You can change the switch without rebleeding the system as long as you are fairly quick and no-one touches the brake pedal. Don't forget to put a wrench around the 4-way connector to take the strain or you can seriously twist up the pipe work trying to undo the switch. But as Guy said, the new ones seem to burn out pretty quickly, so put a relay in the circuit to take the load off the switch contacts.
Mike Howlett

Somewhat surprising - or at least I was surprised - one can remove the pressure activated brake light switch without all of the brake fluid running out. At least not fast enough to cause a panic. If just swapping over, you do just that, and then bleed some fluid off past the threads to get rid of any air bubble. I think if I was leaving it off for any length of time I would fit a stopper of some sort. But I wouldn't drive it like that!

There was an article in MASCCot a little while ago, comparing the internals of the original and the copy switches.

(Sorry Mike, cross messaging!)
Guy Weller

For those who aren't MASC members, any chance of summarising the results?
Dave O'Neill2

Mark,
as has already been put you can snatch fit one, wet rags and water nearby are always handy when dealing with brake fluid

about 3-4 years back I fitted a new brake light switch and I then found out because someone stopped to tell me that the brake lights weren't working - they were but only when I pressed hard so be aware when testing the switch to press the brake pedal lightly as you might in actual use

I replaced that switch with another new switch and that turned out to be almost as bad a third new one, fitted a couple of years ago and it works fine so perhaps the newer stock is better or it's the common problem of new electric parts lottery/roulette
Nigel Atkins

Sorry Dave, I wasn't meaning to be secretive!
I would have to go and find it to give it proper justice, but I think it was by Alan Anstead and it showed, illustrated with photos, the differences in construction of the original "quality" item from Lucas as compared with the copy ones now produced. Detailed differences in the size and construction and accuracy of the contacts. I think the conclusion drawn was that if you can carefully dismantle and repair an original it was likely to long outlast the cheap replacements.
Guy Weller


The bnew ones have different internal circuit connection which soon burn out with loading.

I bought a new switch 12 months ago and fitted a relay.
No problems since.
Gavin Rowles

How about a new switch and LED brake lights?
No relay to wire up and a good feeling inside as you are helping to save the planet (well the human race really as the planet will survive in one state or another) with LED lights!
Just a thought
Dave
Dave Brown

from what I've read I'm not sure LED lights for brakes light are that successful

you can get led bulbs that replace the traditional bulbs and fit as normal but bear in mind the rear light and brake light are combined in one bulb on our cars, you can also get expensive complete panels to replace the full back light unit with indicators too

now I've got a modern switch that works I don't see the need to go any further on mine, at the moment at least, I'll probably find the brake lights have stopped working now I've put this
Nigel Atkins

how about a good original old switch that was saved from a scrapper? Lucas must have made a couple of million of these during the sixties and early 70's, almost all BL used them...
David Smith

Personally, I would have more faith in a secondhand switch than a modern replacement.
Dave O'Neill2

Twas not me!
The article on brake light switches was in the June 2011 issue of Mascot. Its author was Dr J.Davies.

I have had to change a brake light switch in a car park at Florence (Italy) when failure of the switch left me with permanent brake light illumination.

I placed a piece of carrier bag over the brake master cylinder and beneath the brake master cylinder cap.
I then carefully removed the switch with one hand and replaced with new in the other. As one came out one went in. I had minimal spill. Best to remember to remove the carrier bag. There was no need to bleed.

I run LED stop / tail lights. They respond fractionally quicker to the pedal and are not prone to shock failure as with a normal bulb on our much potholed roads.

Alan
Anyone fancy the Stelvio Pass in September.
See www.masckent.org
Alan Anstead

Sorry Alan, for wrongly attributing it to you. But I recall it was just the sort of thing that you may well have written. And sorry too to the rightful author, if Dr. Davies is here watching. I did go to look for it but was thinking in terms of a few months ago, rather than back in 2001! Doesn't time fly! And, in looking back through back copies it is so easy to get distracted and end up with re-reading everything!

I didn't find anything on front wheel bearings though. It must be banned topic!
Guy Weller

Hi Guy
You are so correct. Time flies.

I keep an index of the tech articles in Mascot as I get a lot of tech enquiries, and other diverse enquiries, as the enquiries link on the Masc website comes direct to me.

I was surprised the article was not more recent.
Once WW3, on other parts of the BBS, recedes and there is some sort of definitive result, with regard to front wheel bearings, I will try to get an article produced, by someone, for Mascot.

Alan

www.masckent.org
Alan Anstead

This thread was discussed on 12/04/2013

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.