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MG MGA - Details of the brake switch?

Haven't driven the A for a while, but did so yesterday. Started up great, as usual, but I noticed the brake lights were on all the time. I pressed the brake a couple of times, but still the lights stay on. I think it is the brake switch, which I think is on the 4-way union. Anyone had a problem with the switch? Anyone know how to fix it?

Thanks,

Ian
Ian Pearl

Hi Ian. You are correct. The brake switch is on the 4 way hydraulic union. Check to make sure that the 2 wires going to the switch dont have small strands of wire from the 2 terminals touching each other. This would essentially short out the switch, making the brake lights stay on constantly. If the brake swith terminals have no such short, then the switch is internally shorted, and will have to be replaced. Usually, the switch can be replaced without having to bleed the brakes. Just change the switch as quickly as possible, to avoid fluid loss and possible intrusion of air into the hydraulic system. Hope this helps. Glenn
Glenn

Ian,

Generally these more recent copies of the hydraulic brake light switches cause all sorts of problems. I don't know whether you can fix them, but they are relatively cheap to replace. New ones can very often fail shortly after installing them. They fail to work, only work when you push hard on the pedal, fail closed so the lights are on etc.

In my opinion I think you are better of to just disconnect the wires from the brake light switch and connect them to a mechanical switch located inside the car. Use a brake light switch similar to the rear brake light switches used on some motorcycles with a spring you pull to activate them. With a simple bracket you can mount them in the pedal box area in the car to the brake pedal. No need to drill any extra holes. You can then have the switch adjusted so that the brake light comes on as soon as you touch the brake pedal.

If you need any more info email me.

Rod
Rod Myers

Ian

This topic was discussed at length last year and is perhaps worth a trawl in the archives. One thing that did become apparent was the trouble some owners had(myself included)in undoing the switch. Not much space down there, especially for those of us with right hand drive cars. I ended up having to remove the 4-way union and placing it in a vice to hold it while I undid the switch. Fortunately most owners seem to get it undone insitu.

Best of luck and not too many cuts to the hands!

Steve
Steve Gyles

Ian.
I have heard that silicone brake fluid will eat the inside of the switch and short it out. This must be true, because after I changed to silicone fluid I have changed the switch about once a year. I am now using a General motors switch mounted on a braket working off the brake pedal. It works very well and the lights go on as soon as I touch the pedal. The hydralic switch takes much more presure to turn the lights on. That means you are already stopping before the lights go on. Check around, I have been several articles on this.
Jim.
James Jensen

Jim

Here we go on the silicon debate again. I have been on silicon fluid for 8 years now. I have changed the brake switch once and my supplier confirmed it was a bad batch with failures recorded by users of mineral fluid as well.

There is an opinion that the so called problems with silicon fluid are caused by not purging the system completely of mineral fluid before using silicon. In my car I have only ever used silicon and have had no problem with any of the rubber seals etc in the 8 years.

Steve
Steve Gyles

Steve.
Boy I hope I didn't start something. That was not my intent. I know what you are saying. I have read all that stuff too. I have only used silicone since I have totaly rebuilt my brake system. The switch is the only thing I had trouble with. I do like the the brake lights coming on with just a touch of the petal.
I will admit I think there is a problem with a lot of the replacement parts out there. About a week ago I put up posting about the poor rubber parts I found in my water shut off valve for the heater.
This is how I fixed my switch problem.
Jim.
James Jensen

Guys,

Thanks for the responses. I've solved the problem by attaching one wire to the brake pedal and the other taped to my shoe. That way, everytime I brake, the two wires make a connection and hey presto! Trouble is, I keep forgetting to take the wire off my shoe and fall flat on my face when I get out of the car!!

Only kidding...I'll have a go at the switch this afternoon and let ya know what I find.

Thanks again,

Ian
Ian Pearl

Ian - I like your solution, eloquent simplicity (even if it is hard on the face).

I am going to dip my oar in on this discussion. I too have had the brake light switch on our TD fail after installing silicone fluid, that is 20 years after I installed silicone fluid. Since, as far as I know, the switch was the original one in the car, which means it probably would have failed even if I had left the original glycol fluid in the system. I also had the switch fail in our MGB 8 years after installing silicone fluid. On the MGB, I switched over to a mechanical switch, which failed after 1 week. Since the mechanical switch was nowhere near the silicone fluid, I think we can rule that out as the cause (unless someone wants to make the connection that it was in contact with the "brake" pedal, therefore...). My point in all of this is that the business of silicone fluid causing failure in the brake light switch is nothing more than a red herring that was started by one of the after market manufactures of replacement switches to take the spotlight off of their wimpy switches. I cut open the mechanical switch that replaced the original Lucas brake light switch and what I found was cheap crap, probably the worst I have seen in my 40 year career in electronics - it wouldn't have held up under a flashlight bulb, much less a 21 watt brake light bulb. I have also purposely contaminated the contacts of a open frame relay with silicone brake fluid and then hooked it between my fuel pump test stand two brake light bulbs. Continual on and off operation of the relay for several hours showed no detrimental effects of the fluid. This is because there is none. It is common to submerse high power relays and switches in insulating oil (be it silicone, PCB, or whatever) to cool them and they operate just fine in that environment. Our brake light switches will do the same thing if brake fluid, either silicone or glycol leaks past the diaphragm onto the contacts (however, once past the diaphragm, the fluid will continue its way on out of the switch and then you would have a much bigger problem than brakes lights that don't come on or go off.

The problem that we are dealing with is, pure and simple, lousy replacement switches. It would be nice if we could all band together as Barney Gaylord suggests and force the manufactures to produce switches that will do their job and last like the original Lucas switches, but that is not going to happen. For that reason, I corrected my problem by installing a relay and arc suppression circuit between the switch and the brake lights. Since then, I have not had a problem in either car. Anyone interested in doing this installation in their car, can see the instructions and parts list at: http://www.omgtr.ca/technical/brakelightrelay/brakelightrelay.htm
Cheers - Dave


David DuBois

Do I tempt fate and report an original Lucas switch still going strong after 46 years ? No, that would be too much.
dominic clancy

Hi folks. My original brake light switch failed in 1981 and was replaced with another lucas one. The second Lucas switch failed about 12 years ago, and was replaced with a generic brand, american made replacement switch. (for a Chevy, I think) This switch has been run exclusively with silicone brake fluid since it's installation, and is still working perfecly. Just thought I would add fuel to the (silicone) fire! lol, Glenn
Glenn

Dominic and Glen - You have just proven both of my points. The old Lucas switch, that was made of sturdy parts may well last another 46 years. Glen, Your situation pretty well proves that silicone fluid is not what is causing the switch failure. Cheers - Dave
David DuBois

This thread was discussed between 14/04/2005 and 16/04/2005

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