MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

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 MGB Technical - Brake Light Switch

Here's what the switch looks liek taken apart. Am I missing a contact inside here?

Dan Hiltz

Dan - If you were to lightly sand the disk under the two copper contacts, you would find that the disk under the two copper contacts is also a copper disk that has become oxidized. Cheers - Dave
David DuBois

Dave, you are correct. I had to pry up the contacts and remove the disc and spring to clean both thoroughly. Thanks!
Dan Hiltz

Dan - You might want to consider a relay/arc suppression circuit for the switch. Being an original switch, it has lasted far longer than the ones sold today (I had one last all of 2 weeks), and adding the relay will ensure that the switch will last nearly forever. See the article, Brake Light Relay in the Other Tech Articles section of my Homepage at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

My hydraulic switch lasted a year before I started getting concerned about late and partial operation unless the pedal was pressed quite hard. When fitting that one, and being aware of complaints about these switches, I fitted a tell-tale in the cabin so I could keep an eye on it. I complained to the supplier and their first response was "They all do that sir, that's why there was the change to mechanical switches" and also mentioning the possibility of air in the lines (irrelevant). The second attempt at explaining the problem elicited the suggestion that earthing of the rear lights was to blame - again irrelevant. Finally they sent me a replacement switch. I certainly wasn't going to buy another one, I would rather have got a universal type working off the pedal return spring. But I fitted this with a relay and the tell-tale now comes on with barely any retardation of the car. Time will tell if this lasts mechanically, the previous one certainly didn't last electrically.

Out of interest I tested the operation pressure of both switches. The new switch closed cleanly at about 55psi - which was higher than I expected. The old one did nothing even at 95psi, the max from my foot pump.

Opening up the failed replacement and comparing it to the 'original' that had probably lasted nearly 40 years showed a clear difference in construction. The original has spades rivetted to the top of the plastic body, and a pair of overlapping phosphor-bronze springs i.e. pukka electrical contact components inside. A rubber diaphragm (hydraulic seal) pushes against a metal disc, that has a pip, which pushes against one of the springs, and moves it into contact with the other spring, with a wiping action which helps keep the surfaces clean.

By contrast the failed replacement simply has two spades which go through the plastic material and are bent into an L-shape inside. A metal disc simply bridges these. Not only the wrong material for an electrical contact, but no wiping action. A tiny bit of arcing on the one 'contact', and the disc, was enough to render the switch useless.
Paul Hunt

Great quality these days. My '67 B still has the original hydraulicly operated brake switch that it left the factory with. Whenever I go to drive the car, I first press the brake pedal with the ignition switch turned to the run position and watch the ammeter needle. With a minimum amount of pressure, it drops, indicating that voltage is going to the brake lights. RAY
rjm RAY

It is truly unfortunate that today's brake light switches are pieces of junk (one lasted all of 2 weeks for me). Even the Ron Francis heavy duty switches had premature failures in them. I am at a loss to figure out exactly why this is true other than 1) manufactures are trying to cut manufacturing costs to increase their profit margin or 2) modern cars all use relays in the circuit to reduce the current being switched by the primary switch. Or maybe is a little bit of both.

Like Ray, I had an original switch in our TD that worked fine until about 10 years ago. Once I changed it out, I was lucky to get more than 6 months use from the switch. I finally resorted to a relay with an arc suppression circuit on it's coil (probably over kill, but by then I was paranoid). The paranoia also prompted me to install a tattle tail light in both our TD and MGB, so I know when I am getting power to the stop lights. Cheers - Dave
David DuBois

I found that me switch didn't work, unless I stomped on the brakes fairly hard.
Did this mod to the car and problem solved.

http://www.mgb-stuff.org.uk/saga19.htm

Herb
Herb Adler

I have had the same experience with the so called lucas replacement switches.I was a fool and bought two. Everything about them the gauge of the wire,how they are attached, the contacts etc. are junk compared to the originals. I rebuild the old ones until the plastic and metal gave out. Does anyone know of an aftermarket one that will fit and be reliable.74B and 73GT
B Stone

B Stone - The pedal operated switches are the worst of the lot. You could get a standard micro switch and make up a mounting inside the car to position it properly over the pedal shank. The best bet though, is to get the replacement switch from Moss or else where and then make up a relay/arc suppression circuit (or purchase one) and install it with the switch. See the article, Brake Light Relay in the Other Tech Articles section of my Homepage at: http://homepages.donobi.net/sufuelpumps/ The relay/arc suppression circuit will make the worst switches last a lifetime. Cheers - Dave
David DuBois

Or led stop/tail "bulbs"
Michael Beswick

I have experienced a "lucas" replacement pressure switch that became brightness control of the brake lights. This would only happen when enough preasure had been applied to the pedal to cause an emergency stop.
I rummaged around in my old parts box for the real old lucas pressure switch, cleaned it up, fitted it up and all's well.

New does not mean better!
Richard Thompson

So yesterday I was almost rearended several times to find out that my new, which means cheaply made, brake light switch had failed again. I know we can modify with relays and the sort to piece these things together, but why should we! We as consumers should not have to accept such life threating critical parts and we pay premium prices for this abuse. At what point is the distributor and manufacturer responsible to stop cutting corners in the name of profit and provide a part at least to original standards. After all as much as we critize Lucas, my original switches did last 30+ years. It's not like a piece of cheap chrome plating. Mine came from the E-bay site selling mg parts with NOS next to the parts So naturally you think you are getting something that is of original quality.
B Stone

B. Stone - "We as consumers should not have to accept such life threating critical parts and we pay premium prices for this abuse. At what point is the distributor and manufacturer responsible to stop cutting corners in the name of profit and provide a part at least to original standards."

I agree with you, however let's look at the other side of the coin. In modern cars the brake lights are controlled with a relay or are LED lights that draw very little current or both. Husky switches that can handle up to 2.5 - 5 amps of current are no longer required. Most relays used in modern cars draw a maximum or 0.085 amps, which today's brake light switches can easily handle. Much as I rant about today's crappy switched, I don't think that the manufactures are going to produce switches that will handle up to 5 amps with ease, only to sell, what, maybe 50 switches a year? And as much as I resent this situation, there is not much we can do about it.

Whether we like it or not, our cars are anachronisms and are no longer catered to. If you have an early car, with a hydraulic switch, you can get a heavy duty switch from Ron Francis Wiring at $30 plus shipping and which I have heard 1 or 2 reports of them failing prematurely. For the late model MGB, with the mechanical switches you can opt for a standard microswitch and jury rig a mounting for it as detailed in the link that Herb linked in his post. I chose to use the standard hydraulic switch for our TD and the standard mechanical switch for our MGB and made and installed a relay/arc suppressor circuit on both cars. I also wired in a tattle tale light on both cars that tells me whenever voltage is applied to the brake lights. It has been more than 10 years since I did this modification on both cars and have not had a single failure in that time. Cheers - Dave
David DuBois

" but why should we! "

Exactly, but what choice have you got? As David says if you can't get an NOS switch you either jury-rig some heavy-duty switch, or fit a relay to the standard switch, or fit LED rear lights which have a much lower current. I've gone for the relay option as LED lights are many and varied and the jury is still out on their effectiveness including the lower wattage not dazzling following drivers in the wet, and there being enough differentiation between tail and stop.
Paul Hunt

I'm not be critical just pointing out, sorry B Stone but you made a mistake by assuming NOS meant original NOS as no age meaning, it could be old stock (i.e. stock that has been held beyond a certain stock period) that is only from this year, last year, the last two years, etc.

I've always put on this forum and others that as a generalisation classic car owners are tight fisted and want things on the cheap as they rarely actually use the cars, certainly the case in the UK

perhaps if we banded together and complained to our clubs and suppliers some properly made brake lights would be commissioned but I bet most owners wouldn't want to pay the premium and still buy the cheap crap from others

I've had in the last 7/8 years hydraulic brake light switches that have both worked well and not worked well and the same with the replacements, the plastic pedal ones have been particularly useless bursting apart in a matter of weeks or day (those were from Triumph suppliers)

unfortunately I lost the details of the chap who had a very casual trade in genuine NOS Rover parts from decades ago, all the parts I got from him including the rubber parts fitted and worked as they should
Nigel Atkins

My (probably) original hydraulic brake switch has gone high impedance. I can see volts at the rear bulb holders, but not enough current to light the bulbs.

Can these swtiches be taken apart and cleaned up sucsessfully? I had a look in the archive but didn't see anything on it. I'd rather refurb then buy a new one and go the relay route, but if needs must...

David.
Dave Smith GT

How much voltage? If you get a lower voltage on the green/brown wire at the switch than on the green at the switch then the switch is bad - assuming it isn't bad connections between the wire connectors and the spades. Voltage drops anywhere else along the circuit are bad connections in the wiring. If you get 12v at the holders but the bulbs don't light the problem is in the holders or their earthing. You must take all voltage measurements with the bulbs in and all connections made i.e. attempting to light the bulbs, anything else will give you misleading results.

The hydraulic switches are not serviceable.

'NOS' stands for New Old Stock, which if correctly applied is a genuine original part from the original manufacturer i.e. to the original quality, the age is largely irrelevant. It is usually applied to parts that were manufactured during the production run of the model, but manufacture could have been continued after a given model ceased, if it was used elsewhere. It should not be applied to a copy or pattern part from another manufacturer that never supplied the factory, no matter how long ago it was manufactured. Doesn't stop the unscrupulous claiming it though.
Paul Hunt

Paul,
I did replace a corroded three way bullet connector joiner at the back of the car which I hoped would be my 'ah-ha!' moment, but sadly not. Taking the spade connectors off the switch and touching them together gives nice bright brake lights, so the wiring is still good. I'll use a relay and diode on the new one.
Dave Smith GT

>>'NOS' stands for New Old Stock, which if correctly applied<<
Paul some retailers seem to apply an updated version of that - same way some youngster call our cars vintage rather than classic

meaning change over time you have to confirm you're using the same meaning to avoid errors unless you dealt with the person/organisation before and know their terms of reference
Nigel Atkins

I haven't run into this problem simply because the brake light switch, in my '67 B, is the original unit. I dread the day when it finally gives up the ghost. So much of what I install, on customers cars, is made to very poor standards today. Frankly, I think that we were spoiled by the high level of craftsmanship that originally went into our cars when they were initially assembled. This seems to have become a lost art. Today's cars are not designed to last beyond a couple of years. We still live in a disposable economy. When I tell someone that I've owned my car for over 41 years they look at like I'm crazy and ask why I don't simply get a new car every two years. My reply is that my car continues to give me great pleasure and that I haven't driven another car that can match it quality, reliability and pure driving fun. Of course, it doesn't hurt that I do all of the preventive maintenance and repairs on the car myself. No one else drives it and no one else works on it. RAY
rjm RAY

Just replaced a new switch and put in the Dave Dubois relay. Very easy fix. Now to see how long the new switch holds up (hydraulic switch)
Bruce Cunha

The original hydraulic switch on my car lasted 45 years. The replacement lasted one. I got another of the present offering and fitted a relay. I was really scared when I found I was in danger of being rear ended and put an LED tell tale in the cockpit. This is on the relay contact in parallel with the lamps so if it working the relay is actuating.
Both failed switches show continuity with a DVM but will not pass heavy current.
Stan Best

Hi,

Hydraulic brake switch on my 1958 Wolseley. Still going strong, light pressure on the brakes and the lights light.

Not bad for a 55 year old item. Wish I could say the same about myself.

Herb

Herb Adler

The original switch lasted 30 years in my car. The replacements about 6 months until I found a used one and installed a relay to protect it.
Glenn Mallory

This thread was discussed between 01/08/2013 and 25/08/2013

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now