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MG MGA - brake lights switch

Hi folks,
I have today discovered that my brake lights aren't working. I bridged the brake switch terminals, with the ignition on, and the lights came on. I now need to replace the switch. On many occasions I have read about poor quality switches on the market, and my question is where can I buy a good quality switch? Does anyone know of a good source? Your help is much appreciated.
F. Camilleri

Hi - I don't know where you can get a good quality switch. But your bigger problem might be removing the old switch without damaging the brake pipes. I went down the route of putting in a mechanical switch operated directly by the brake pedal. Good luck! Martin.
M Hooper

Search the archive, there was a recent thread on a good quality modern replacement. It's not unique to the MGA
dominic clancy

If you are useing dot 5 that could be your problem. Ron Francis Wiring has a brake light switch that they say will stand up to dot 5. I have not tried one yet.
Lyle Jacobson

General replacement brake light switched are junk and will fail in a short period of time. There are two solutions to this situation. 1) get the heavy duty switch from Ron Francis Wiring as Lyle suggests above - the P/N is SW-32 or
2) make and install a relay/arc suppression circuit. For instructions on making and installing a relay/arc suppression circuit, see the article, Brake Light Relay in the Other Tech Articles section of my web site at: Cheers - Dave
David DuBois

1.) First of all, as far as I know there has never been a brake switch failure as a result of using any particular type of brake fluid. If the brake fluid could ever get to the switch contacts it would be leaking on the ground. I thought that idea was settled years ago.

2.) The bad switches fail because of poor quality cheap contacts. I would never recommend a relay installation in attempt to save a bad switch. Buy a good switch and be done with it. The trick of course to figure out which switches may be bad before you buy them.

3.) I have offered multiple times to compose a tabulated list of bad switches, but so far no one has bothered to send the information when one fails. Apparently most people toss the failed switch in the trash first, and then some people complain loudly in public, but most people can't be bother to notify the supplier when the switches are bad. That pretty much guarantees that you will have a forever continuing stream of bad parts. If that's what you want, then stop complaining. If you want good parts, then do something constructive.

4.) Since no one is helping so far, my best currently available move to get the ball rolling is to post a web page listing possible sources for these switches. Until someone says otherwise, they will all be assumed to be good quality parts. If you think you have a bad one you need to speak up so it can move from the White list to the Black list (so to speak).

5.) Any one individual bad switch does not make a class action case. The suppliers will keep selling parts as long as people keep buying them and very few are returned. To do any good at all we need multiple reports of bad parts from a named source. Also people should be sending the bad parts back to the vendors, or at least notifying the vendors that the parts are bad.

Is anyone getting the message yet? Start here:
Barney Gaylord

Lyle, the story that silicon fluid can cause this is rubbish! The only way that this can happen if someone converts over from standard to silicon and doescn't completely clean the brake system.
Gary Lock


After reading all your inputs, and also went through other threads on the archives, I have today ordered the brake switch SW32 from Ron Francis Wiring. I convinced myself that that's the best way to go. Many thanks to all of you who contributed to my thread. I am only hoping that the old switch will come out easy enough, we'll see.

F. Camilleri

Frank, let us know what you think of the SW32 switch. Actually, I have a MGB master cylinder in my '57 MGA with B brakes so I just have problems with the poor MGB switches from Moss. Pictures of the conversion are on the inter net. Google Lyle Jacobson 1957 MGA.

Gary, The promlems I've had is with my old Fords I did change the systems from dot 3 to dot 5 and the systems were cleaned of all dot 3 and new parts installed. I've talked to a lot of other old car owners that have the same problem.

Lyle Jacobson

Lyle, I will indeed let you know what I think about the SW32 switch. However, it might take a while as I have to receive it from the USA, which is on the other side of the globe for me. I'll come back to you.

F. Camilleri

Coming back to this thread, Lyle Jacobson asked me to report back to say what I think of the new switch Pt. No. SW32 from Ron Francis Wiring. Today I removed the old switch, which was very tight to unscrew. I managed to wedge the bronze cross piece against the chassis frame, and the switch came out easy enough. The new switch fitted perfectly, its thread was OK. I put a little pipe thread tape around the thread and I screwed it in by hand. I then tightened it with a socket on a long extension. No leaks anywhere. The brake pedal now only requires light foot pressure for the brake lights to come on. No need to bleed the brakes. I am now hoping that, it being a heavy duty switch and is compatible with silicone fluid, will last quite a long time. That remains to be seen.

F. Camilleri

I have been running one of Ron Francis switches for over two years with no problems.

Bob Wrenn

What did you guys do for a wire connector on the SW32 switch?
Barney Gaylord

Barney, the wire connector comes with the switch. It is made of a plastic slide-on insulator and two special brass sliding female wire connectors. I attached two short pieces of wire, one to each brass connector, then they slide inside the plastic insulator and click in place. On the other end of the two wires I fitted two ordinary insulated male slide connectors. The plastic slide connector then slides onto the switch connections, while the other two ordinary slide connectors were connected to the two existing female connectors which were already on the ends of the two wires coming out of the loom. Hope this helps.

F. Camilleri

Original brake switch has set screw posts to connect bare wire ends.
Barney Gaylord

Like Frank, my brake light switch began failing a couple of weeks ago. I suspect that the extra load from the third brake light that I installed last year hastened its demise. I doubt that that brake switch that I removed was original, no numbers, hex sides with screw terminals as original. I purchased a SLS273 made by Standard Motor Products. The box said made in the USA. It has a body similar in shape to the Ron Francis SW-32 switch, but uses the original type screw terminals. Also the Francis switch advertises a low pressure needed close the circuit. I hooked up the SLS273 to my compressor and slowly increased pressure. The SLS273 switch reliably closed and opened at an 80 lbs. threshold.

When I rebuilt my brake system and changed over to DOT5 a few years ago I had all of the wheel cylinders out, the three-way connector on the rear axle, the hoses, clutch slave cylinder and the master cylinder apart for cleaning and flushing. The one connector I did not remove was the four-way fitting with the brake switch. In pulling the old switch it looks like the is some gunk at the bottom of the threads. I cannot tell how much, but I do plan to pull the fitting when I replace the front brake lines this spring.

Lastly a question regarding bleeding the brake system and specifically the brake switch. Since the switch is a blind hole and is above the brake lines is there any need to be concerned about the possibility of an air bubble getting trapped in the switch. As a precaution I pre-filled the switch with brake fluid and used a thin piece of plastic to hold the fluid in place before inserting the switch into the connector. I also carefully cleaned off the top of the connector and topped it off with a spot of fluid.

Other than getting the old switch loose, it was a pretty straight forward replacement. I don

Thanks for the information Frank. I'll order a SW32 to keep in my '57 Ford for when the next time it stops working. It's easy to replace on the road. I replaced the one that's on the car now about 6 months ago.
Lyle Jacobson

I've used a couple SW-32 switches. One recently went bad but it did last several years of daily use.

I also agree that fluid has nothing to do with anything. Modern brake parts, as far as I know, are required to work with all types of standard brake fluids - 3, 4, 5, and 5.1.

John, the gunk below the brake switch could be the reaction of DOT 3/4 and 5 along with any contaminants. When the two fluids are put together they don't seem to do anything interesting, but introduce a bit of moisture or other contaminants and you get a nasty goo forming everywhere.
Steve S

I really like the idea of the modern, heavy duty switch. Not really a fan of the modern, plastic connector. Wish there were a way to make it look more like the original unit. I guess you could leave a failed original in place with dummy wires going to the loom, and plumb in the modern switch someplace where it won't show (or use the pedal mounted mechanical). But I'd hate to do it that way.
Del Rawlins

Use a rubber boot over the plastic connector. You can probably also cut the connector down a bit. I've thought about doing this but never got around to it.
Steve S

I have been going through a brake light switch every season. I use silicone fluid but it has nothing to do with the failures. I have gone through the Moss switches, the Harley switches (they use silicone), and finally the Ron Francis switch. When I cut them open to see what caused the failure, it is always the contact points are burned. I talked to Ron about this and he suggested to adapt his mechanical switch to the pedal assembly and be done with it. That's what I'm doing right now.
A Baran

I've replaced my brake switch twice in the past 5 years. Both times with an echlen switch from napa. The first one lasted for 1 1/2 seasons. The most recent one has already lasted more than twice as long. Was I unlucky the first time or lucky the second time?
Andy Bounsall

The Ron Francis mechanical switch will solve all of these problems. Get a 2 1/2" corner bracket, drill out the holes to 5/16", and shorten one leg. It bolts to the master cylinder base plate.

A Baran

I just find it astounding that no modern manufacturer can make a better switch than a Lucas unit from the fifties.
Del Rawlins

The only modern manufacturers are in China and they are building down to a price.

I'm sure that if the parts retailers weren't making 1000% profit, they could make reliable parts.
Dave O'Neill2

Hey all, interesting thread. Don't I remember that in order to prevent or minimize the arcing and subsequent points burning in such a switch a capacitance across the contacts would help? If so, what would be the value? Tom
Thomas McNamara

This thread was discussed between 03/02/2012 and 04/03/2012

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This thread is from the archive. The Live MG MGA BBS is active now.