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MGB Technical
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Thread: Brake light switch
Posted 01 September 2017 at 11:01:49 UK time
Andy Tilney, Cumbria

Brake light switch recommendations,(hydraulic type) I am sure I know what the answer will be, but has anyone found a supplier for one of these, that will last more than a week, also have any of you chaps used an OE one from another vehicle manufacture, I was thinking perhaps some of you in the US.

Posted 01 September 2017 at 13:37:30 UK time
Allan Reeling, Shropshire, United Kingdom

Andy, I made a simple bracket and put an basic contact plunger type switch activated by the brake pedal itself, inside the car.

Posted 01 September 2017 at 16:04:25 UK time
Andy Tilney, Cumbria

Allan, That was going to be my next plan, if I don't have any luck with a new switch, if I had thought about this parts supply problems 25 years ago I would be worth a fortune today, and I now wish I had kept all the 3.5 ltr and 3.9 V8 engines and 77mm gearboxes, I took to the scrap yard, not to mention enough mini gearboxes to sink a battle ship, hindsight is a wonderful thing.

Posted 01 September 2017 at 18:32:31 UK time
DW DuBois, USA

Andy - the only brake light switch on the market today that seems to stand up to the rigors required of the switch is the SW-32 from Ron Francis Wiring at http://www.ronfrancis.com/ The draw back to that is the price of $30.95 plus shipping. The other avenue would be to make up a relay/arc suppression circuit to protect the brake light switch. See the article, Brake Light Relay in the Other Tech Articles section of my Homepage at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave

Posted 01 September 2017 at 20:47:08 UK time
Andy Tilney, Cumbria

Thank you Dave for your reply, I will make a note of this and if I cant find one here in the UK, I may well contact this person, I am happy to pay $30.95 for something that works, for me reliability (and originality)is my main concern,

Posted 02 September 2017 at 05:16:05 UK time
DW DuBois, USA

Andy - Quite frankly, the relay/arc suppression set up is the only way to insure that the switch doesn't die on you. I had a problem with brake light switches on both our TD and MGB, going through several switches on both cars. I finally sat down and put the relay/arc suppression circuit together and have not had another brake light switch fail in over 10 years on cars that are driven daily.

As for originality, the Ron Francis is not going to look original due to the socket that goes with it unless you solder wires onto the pegs on the switch.

Posted 02 September 2017 at 13:09:09 UK time
Allan Reeling, Shropshire, United Kingdom

Andy, another way to go to reduce the contact load on the switch is to convert to LED lamps. Wouldn't help of course the the recurrent failure is of a mechanical nature!

Posted 07 September 2017 at 13:05:21 UK time
G Britnell, Lancashire, United Kingdom

I put LED Stop/Tail lamp bulbs in mine because of recurrent failures of replacement hydraulic switches. Not had any problems since. This was 3 or 4 years ago.

Posted 10 September 2017 at 11:09:46 UK time
Glenn Mallory, New Mexico, USA, gmall18073@aol.com

I also installed a relay and this eliminated the switch failures.

Posted 12 September 2017 at 15:04:01 UK time
Andy Tilney, Cumbria

After some hunting around I managed to locate some Genuine Lucas NOS brake light switches, I ordered it yesterday, and it came first thing this morning, the Lucas part no is SMB 423,which cross references to the number stamped on the back of my original switch which is 34542,it came in a Lucas bag made in the UK and a date stamp of 23/97, and it cost 3.00 + postage, the firm I bought it from are -LMS (LICHFIELD)LTD 5 Watling Street Lichfield WS140PL,PHONE NO 01543480600.
Web address www.lmslichfieldltd.com, the gentleman I spoke to in the stores said they had quite a few left in stock, but had sold a great deal of them this year, its all ex army stock and they have allsorts of stuff for sale, even if you are not after a brake light switch its worth a look at there web site, so hopefully that's my brake lights sorted, and hopefully this switch will last 48 years like the last one,

Posted 12 September 2017 at 15:09:04 UK time
Andy Tilney, Cumbria

I forgot to add this to my last post


Posted 13 September 2017 at 15:40:58 UK time
Tony Brough, Birmingham

Thanks for the update and info Andy.

Ive just ordrred a couple!

Posted 13 September 2017 at 21:46:55 UK time
DW DuBois, USA

Andy - Go ahead and put that switch in, but then make up the relay/arc suppression circuit, posted on my Homepage, because, I will guaranty that that switch will flake out on you - that is the same switch that convinced me that it needed a relay. Cheers - Dave
PS - If you install LED brake light/tail lights, the switch should work fine.

Posted 13 September 2017 at 23:50:54 UK time
Andy Tilney, Cumbria

Dave are you saying that you fitted Lucas NOS SMB423 switch made in 1997 to your car, and it failed after a short time, or are you saying that you fitted one that looked like it, and it failed.

Posted 14 September 2017 at 00:00:03 UK time
Dave O'Neill 2, West Midlands, United Kingdom

You can tell the modern reproductions, as the body of the switch is quite a lot smaller than original.

Posted 14 September 2017 at 09:32:33 UK time
Charles9, uk

Following Andy 's find of LMS I have today just ordered 2 brake switches by telephone. The very helpful "Diane" confirmed they were genuine old lucas items (I accept no liability if this comment is not valid) & that there seemed to be quite a lot of interest recently. I said that their name had been posted on our forum & she recalled Andy's name.

Posted 14 September 2017 at 17:10:02 UK time
DW DuBois, USA

Andy - Regardless of the part number, the one you show in your picture is not new old stock. The original Lucas parts came in a red box. The green box (or in your case plastic bag) is not new old stock in spite of what you were told. Cheers - Dave

Posted 14 September 2017 at 20:35:41 UK time
Charles9, uk

When I ordered my switches this morning "Dianne" said they were in red boxes - until they arrive I can't comment further!

Posted 14 September 2017 at 23:03:48 UK time
DW DuBois, USA

Charles - If in fact you get the switch in a red box (preferably one that is beat up and somewhat faded, you may have gotten a new-old switch - said parts like that are few and hard to come by). I have become very skeptical of advertised new-old, Lucas parts over the years. I would seriously suggest making or having someone making the relay/arc suppression circuit to install with your new switch. I have made and installed the above circuit on our TD and MGB and over a hundred of them for customers. I have not had any loss of a brake light switch since making and installing them on our cars and have not had any complaints about over 100 of the circuits for other people. The circuit is easy to make up and the cost will not much more the parts to make the circuit (or have someone to make it up for you if you don't feel confident to make it your self). Cheers - Dave

Posted 15 September 2017 at 04:03:20 UK time
Bruce Cunha, California, USA

When you do a search on their web for SMB423, it does show it with a red box.

That is a interesting web. A lot of various switches. I even see a fuel gauge that looks like one from a B. (well, except for the fuel pump emblem on it). Various toggle switches (two position). Later B toggle headlight switch. Headlights, etc.

Posted 15 September 2017 at 12:25:29 UK time
Andy Tilney, Cumbria

Lucas parts and red boxes, Lucas changed there packaging from red to green in 1994 and the company was sold in 1996, so if it is boxed red or green does not always mean that its not NOS,

Posted 15 September 2017 at 12:40:38 UK time
Tony Brough, Birmingham

Mine have just arrived 03 95 complete with spade fittings and covers 😁


Posted 18 September 2017 at 08:18:41 UK time
Michael Beswick, Hertfordshire, United Kingdom, genesismb@aol.com

Another way of identifying OE switches is that the spades are riveted on, attached to a 'proper' switch mechanism with wiping contacts using 'proper' contact materials.

The copies have the spades disappearing into the moulding to become very crude switch contact, which have no wiping action and are in a material too soft to take the current from the lamps.


After a current (no pun intended) stock item started failing in weeks I replaced it and installed a relay, no problems since.

Posted 18 September 2017 at 08:38:48 UK time
paulh4, West Midlands, United Kingdom

It's not very clear but the image from LMS does appear that the spades are L-shaped and therefore riveted, but on that from Tony they are not. Could Andy and Tony confirm whether theirs are riveted or not?

Posted 18 September 2017 at 10:08:01 UK time
Andy Tilney, Cumbria

That is a interesting point,about the terminal fixings, I have checked mine and indeed you are correct they are not L shaped and riveted, they are moulded into the plastic, unlike my original which are L shaped and riveted. I will investigate this further perhaps my fortunate find was not as good as I first thought,

Posted 18 September 2017 at 10:49:31 UK time
Andy Tilney, Cumbria

Update on these switches, I have contacted LMS again, and Diane the Lady in the stores checked all the switches they have left in stock, and they all except one, have moulded terminals, irrespective of box colour or date coding, the only one with riveted terminals they have left was in a Green box with a date code for 1984, now I am confused as I did not think Lucas changed to Green packaging until 1994,

Posted 18 September 2017 at 11:00:29 UK time
Dave O'Neill 2, West Midlands, United Kingdom

Maybe Lucas redesigned the switch at some point (not inconceivable) and the recent copies are based on the new design of switch, although poorly made.

Posted 18 September 2017 at 11:20:46 UK time
paulh4, West Midlands, United Kingdom

Diane has said the following, in response to a question about the terminals:

"We think we know what you are after, our switches have conventional terminals.

"We know the very early ones had rivetted terminals we have seen these but have no more in stock."

Following on from Dave's comment, really one would need to open up one of these and see what was inside. I wouldn't mind spending 4 to do that, but not 10 i.e. inc P&P. However as I'm running-in the V8 at the moment and looking to do some miles when I can, collection might be a possibility.

Posted 19 September 2017 at 15:49:46 UK time
paulh4, West Midlands, United Kingdom

The LMS switch is the same in principle as the rubbish ones, but with two quite possibly significant differences.

1: The spades do go through the plastic moulding to become the switch contacts, but it is the cut-off end of them that forms the contact, they are not bent over as in the rubbish ones. This could well mean that the contact 'surfaces' are sharper and cut through any burning better.

2. The material of the spades and the contact disc appears to be different to the rubbish ones - being brass-like rather than alloy-like on the rubbish ones. If they are harder, they it may well resist burning better. Compare with http://www.mgbimages.uk.gridhosted.co.uk/images/blswitch2b.jpg

Continues ...


Posted 19 September 2017 at 15:53:43 UK time
paulh4, West Midlands, United Kingdom

... continued.

I thought I may be able to test this by seeing how the two sets of spades resisted bending, but could not find the one I sectioned a couple of years ago. "Never mind", I thought, "I'll try the replacement I eventually managed to winkle out of the MGOC when their first one started failing in months ..." only to find it has rivetted spades!


Posted 20 September 2017 at 13:51:01 UK time
Andy Tilney, Cumbria

I have managed to obtain another another brake light switch,this is the correct one,(new one on the left original on the right), and came in the box in the photo, if the numbers 9/84 are the date code, then you can not go by the package colour,if not I am totally confused, anyone any other ideas


Posted 20 September 2017 at 13:59:17 UK time
Dave O'Neill 2, West Midlands, United Kingdom


Is the date stamped on the switch body too?

Posted 20 September 2017 at 14:43:50 UK time
Andy Tilney, Cumbria

Just looked on my original switch and its does have 4269 stamped on it, which may well be the date as my car was built in November 1969, the new switch is stamped 1289, if this is the date code I am now even more confused,

Posted 20 September 2017 at 16:57:53 UK time
paulh4, West Midlands, United Kingdom

As LMS were opening boxes to check the spades it's possible they got the switches and boxes mixed up, as they go by part number and they are all the same part number they wouldn't have seen that as a problem.

With the exception of the '780' in Biro your box is identical to mine in every other respect, and my switch has the spades going through the plastic moulding. The only other numbers (apart from SMB423) on my switch are '22E6'.

Andy's are both the same as my 'original' i.e. the spades have triangular bases and are offset wrt each other, which is different to my 2013 second replacement from MGOC. Given that, there is a very good chance that they have the same internals as the original, but to be sure you really need to cut them open :o)


Posted 21 September 2017 at 08:42:48 UK time
paulh4, West Midlands, United Kingdom

Another thing I meant to say is that if 4269 is the date code using week numbers, then it must have come pretty well straight from the switch factory to a November-built car.

Whilst Lucas didn't merge with Varity until 1996 (subsequently bought out by TRW who licenced the name to others) it would be surprising if Lucas themselves didn't have arrangements with component manufacturers by that time instead of making them all in-house, and as such there could be detail differences whilst still conforming to a specification.

I remember seeing the then new logo of the green 'L' on the white diagonal band in the mid-70s and thinking it looked like an arrow going downhill and backwards, wondering if that was to be the future direction of the company.

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