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MG MGA - Brake Light Switch

My brake lights have stopped working and after much testing to find the problem I think its come down to the brake light switch but the symptoms are puzzling. With the pedal pressed the terminal to the rear lights will light up a 2.2W bulb but not a 21W bulb. Obviously some current is getting through but perhaps not enough? Theres load of stuff in the archives on brake lights but I found nothing to cover these symptoms. Does anyone recognize this and is this a definitive test for the switch?
J H Cole

If you bypass the switch do the lights light properly?

Granted they'd be on all the time, but it would quickly give you an idea where to look further I'd think.

Cheers,
Christopher
Christopher Wilson

with low curent situations I generally look at bad or insufficient grounds
Chris Velardi

CW-I've just reached down and connected the two terminals and the lights come on so I guess that means the wiring/ground is OK. Finger points at the switch still?
J H Cole

What kind of brake fluid are you using. I DOT 5 Silicone fluid which has been known to eat brake light switches. At least, I have had to replace mine twice over the years.
Keith Lowman

Wives tale about silicon. My 58 has had silicon for 20+ years and orig switch.
R J Brown

JH - You need to replace the switch. Either get the switch form Ron Francis Wiring http://www.ronfrancis.com/ P/N SW-32 for a heavy duty switch that will last for many years, or get a cheap switch from NAPA and make up and install a relay/arc suppression circuit at the same time. See the article, Brake Light Relay in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ for instructions.

Keith - You need to do the same thing - Silicone fluid is not the problem, replacement switches (other than the ones from Ron Francis Wiring) are junk. You are lucky to have only had to replace two switches. You may be able to get by just making and installing the relay/arc suppression circuit with the current switch, but I have had problems even with the relay when used with an older replacement switch. Cheers - Dave
David DuBois

That sounds reasonable. Every repro part that I have installed as been of less quality that the original functioning part that I removed during the restoration. I still have my original functioning brake light switch that was on the car when I bought it. It checks out so next time I need to replace it I will go back to the original and put the wives' tale to bed. Thanks guys.
Keith Lowman

I have been told that the brake light switches that sre sold now are designed for relays and full current burns them out.
Barry Bahnisch

David I'm not sure if Ron Francis can supply to UK so I'm probably going down the road of standard switch with relay. Holden do a more expensive switch at 19.00 but still can't tell me where its made other than not UK. (A standard switch seems to be about 8.00) I telephoned Bob West-his colleague, and was disappointed to hear that they blame Dot 5 for early failure of the switches. I feel I can't win on this one as I use Dot 5. It really grieves me to have to replace the old switch with a product you know from the start may very well be rubbish especially since it sounds like it may be a pig of a job to do.
J H Cole

Just been looking at access to unscrew the brake light switch and I really don't know how one person without a ramp can do it. Not only have you to use an extended sock to do the unscrewing but you first have to reach down and disconnect the terminals and fit spade connectors for the new switch. I can hardly see what I'm doing let alone reach it to handle the wires -see pic. I've done most things on the car but for the first time ever I may have to give the job to a local garage. I'm full of admiration for the ingenuity of fellow owners that have managed to do this for themselves without a ramp.

J H Cole

This is one of the few advantages of having a LH drive car. Access to the brake switch. In the past, I have always envied the RH drive cars for ease of access to the wiper motor.
Chuck Schaefer

JH - "...was disappointed to hear that they blame Dot 5 for early failure of the switches. I feel I can't win on this one as I use Dot 5. It really grieves me to have to replace the old switch with a product you know from the start may very well be rubbish especially since it sounds like it may be a pig of a job to do. "

At the risk of offending any in the switch manufacturing business, I find that manufactures (at least those in the US) are quick to find and blame a convenient scape goat rather than concentrate on making a product that will stand the test of time. The first brake light switch to fail in our TD (some 20 years after installing silicone fluid) was the original Lucas switch, which I am sure just wore out from normal use. After installing several replacement switches (both Lucas green box units and after market switches in the car, only to have them fail in a couple of months, I finally went with the relay/arc suppression circuit and have not had a failure in 5 or 6 years (still with silicone fluid in the system. This tells me that it is crappy products rather than silicone fluid that is the culprit. Further, I had the same problem on our MGB. And went through the same drill with it. I finally changed over to a pedal operated, mechanical switch thinking that would cure the problem - wrong! That switch failed in a short two weeks and it was nowhere near the silicone fluid (unless the manufacture is going to claim that just being within a 6 foot radius of silicone fluid is sufficient to cause the problem). Again, a relay/arc suppression circuit cured the problem.

My recommendation is to get the relay, diode and capacitor and put the circuit together before changing out the switch. Then do all the hard contortions of installing the switch and the relay circuit at the same time and you won't have to fuss with it ever again.

By the way, silicone fluid was originally produced for the military so that vehicles that sat for long periods of time did not have to have the brake system completely rebuilt before putting the vehicle back into service. It is interesting to note that there has never been anything reported about the silicone fluid destroying the brake light switches in their vehicles. Cheers - Dave
David DuBois

J H Cole, you mention having to fit spade connectors for your replacement brake light switch. I had to replace my brake light switch about 3 years ago and just walked into our local motor factor (Autozone) and picked up a switch like the original with screw terminals. A pig to change; I seem to remember standing on something so that I could reach the switch a bit easier, but I have had no trouble with it so far. So I am wondering if it is the later type with Lucar connectors that folk are finding unreliable. I have had similar problems with replacement brake light switches on my series 3 Land-Rover. These are not hydraulically operated ones like the MGA, but have a brass button to operate them. I have had three fail after about a week of use (12 a time) on a perfectly standard brake light system. In the end I had to repair the broken Lucar connector on the original switch and it has given trouble free service ever since. The suppliers of the failed replacement switches claimed they had never heard of anyone having trouble with them and refused to replace the switches free of charge. I scoured the internet to see if I could find any mention of people having trouble with these switches, but drew a blank. I think there are a lot of, as David in the previous posting puts it, "crappy products" about, but suppliers seem to be reluctant or slow to do anything about it.
Lindsay Sampford

Lindsay - I have had problems with both the Lucar connector and the grub screw connectors. As for the not wanting to do a refund for a bad switch, I can't say that I really blame him. The manufacture is putting out bad merchandise (probably produced by the lowest bidder off shore), and it is the supplier that winds up taking the brunt of the consumers anger - kind of caught in the middle. To make matters worse, to provide a better product (such as the switch that Ron Francis Wiring supplies), the supplier has to charge 3 times what the crappy product costs and the consumer complains about that - the suppler is in a loose, loose situation. Cheers - Dave
David DuBois

I am not sure how many of you know that the correct brake light switch is a tapered threaded fit. I picked up a straght threaded version once and it leaked like a sieve.

The first time a switch went on me it was a sod to remove. During my chassis-up rebuild 12 or so years ago, it was easy to tighten everything up with with no engine in place etc. Little did I know how difficult it would be to get bits like this undone several years later. I ended up disconnecting the brake pipes from the 4-way union and removing it to the workshop vice to get the switch undone.

Lesson learned. My recent switch change took 10 minutes maximum and no bleading required.

Steve
Steve Gyles

Steve- when unscrewing the switch in the car how did you stop the union rotating?
J H Cole

JH

By not tightening it up too much last time I changed it! I had your problem first time round. As I said, I ended up removing the union and unscrewing the switch in the vice.

Steve
Steve Gyles

I can't remember exactly how I did it, but I remember wedging something between the brakeline nut and the chassis. It may hve been a wrench or a screwdriver. It can be done insitu.
Chuck Schaefer

John, I removed the drivers toe board (Steve Gyles tip from the archives) and that gave me enough room to get a pair of molegrips onto the union (directly under the switch) I then used a long bar (vertically in the engine bay) to lever against the mole grips while I unscrewed the switch.
Neil McGurk

Heat helps. I just hit mine with a small propane torch and she came out.
Chris Velardi

I fitted a mechanical switch operated by pedal movement. This was mounted on a bracket secured to the pedal box metalwork and was also wired through a relay also mounted on the bracket. Wires were simply extended from the existing. Don't expect to have to change the switch at all now. The old switch simply acts as a plug on the four way union.
C Manley

Neil

Cor, did I really give such an inspiration tip?

Just a point in support of R J Brown & David DuBois about the false accusations of Silicon fluid being the cause of switch failure; I dismantled my last failed switch and there was absolutely no sign of fluid contamination inside.

Steve
Steve Gyles

I've finally managed to fit a new brake switch. For those faced with a similar problem (rotation of the 4 way pipe union)this may be of some help. From a piece of ms flat bar 25x4 mm cut a length such as it tightly wedges between the most appropriate pipe screw connector into the union and the lip of the engine block/sump. When you unscrew the switch with a socket extension the bar struts against the pipe union preventing any tendency to rotate anti-clockwise. When a new switch is screwed in simply reposition the bar against the clockwise rotation.
On the basis that my new switch is no better than some described above I followed David DuBois's advice and fitted a relay with external capacitor and diode. The only problem and I'm not sure if it a real problem is that the relay makes a surprisingly loud 'click' every time I pressed the brakes. For those up to speed on electrical matters I wonder if this is normal or have I got a duff relay. Brakes work OK.
J H Cole

John, audible brake warning indicator - cool!

Good anti-rotation solution too.
Neil McGurk

This thread was discussed between 10/07/2009 and 16/07/2009

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