MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

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 Midget and Sprite Technical - Brake lights

Is it just a coincidence?
Having just taken up the adjustment on the rear brakes, I find the brake lights no longer come on.

Could it be that with the slack being taken up on the rear brake shoes, it has altered the amount of travel in the master cylinder and contact with the brake light switch is affected?

I don't see the logic of how the brake light switch works anyway. I presume that it relies on mechanical cotact with the top of the brake pedal, so surely, if you depress the brake pedal, it moves it out of contact with the switch.

Checking with a test lamp, there is power going into the switch but none coming out when the pedal is depressed.

Dave
Penwithian

dodgy switch contacts

test by connecting the two wires together with ignition on

if the lights come on, you need a switch (or have dirty connections)

if not, time to check connections down the loom
Bill sdgpm

Dave, to elaborate. The switch is a "normally closed contacts" type that is switched off by the touch of the pedal when you release it.

As the pedal is moved the internal contacts "make the circuit" and the lights come on

unless the switch has expired

If you take the cover off the pedal unit you can see the pedal operated sort nestles in amongst a pile of assorted grunge and grovel, which can encourage the slimy dampy horribley yucky stuff to get inside the switch and cause switch failure

test as I advised
Bill sdgpm

I'v a tested good original switch if you need one, supposed to be a lot more reliable and long-lasting than the modern new replacements.
David Smith

I recently had the same issue and found that the connecting wire for the rear lights had come loose.

Shaun
Shaun

Have you all run mad? My brake lights are operated by fluid pressure.




Aren't they?
Nick

Nick -- its a 1500 they have a switch in the pedal box!
Mick - trying to sort the wiring

Phew! Thank God for that. I thought you had all suddenly been inhabited by aliens.


Still not sure about Bill, of course.
Nick

grok well Nick

I mean you no ill will

but there is much wrong with your planet
Bill sdgpm

Bill,

If I understand you correctly, "test by putting the two wires together with ignition on, if the lights come on then the switch is u/s"

I tried this but no lights came on. However, putting a test lamp across the two wired connections at the switch, the test lamp illuminated but still no lights at the rear. Mmmmmmm.

David, if the (less than two year old) switch has expired, I might well take you up on your kind offer.

Dave
Penwithian

Dave if the lights dont come on at the back when you need to look further back.

FIRST YOU NEED TO CHECK THE BULBS...

Yup, it happens!

IIRC there are two places that may have the open circuit being described:-

The junction of the front and rear loom behind the right hand edge of the dash is one place that can have the bullets loosen. Check the wire that is green and purple, (the brake light wires) and ensure it is pushed into the connector block all the way, both sides

If that is OK go to the back and check the connectors at the back too

You can use the test lamp to check inside the bulb holder for electrickery, if you have it the next bad part is the earth return...

HTH
Bill sdgpm

Tee hee. Where does that come from, Bill?
Nick

two places/sources



and me!
Bill sdgpm

In this case, it is superfluous, but always make sure that the center piece of the switch is actually free to move. It is a "normally closed" switch that is actually turned off by the pedal being released to push it. If the car sits too long, the actuator gets stuck and stops moving out when the brake pedal gets pushed... sorta hard to tell if you are the bloke stepping on the pedal. A bit of silicon spray or WD40 and some time spent encouraging it to move will frequently bring them back to useful life.

This is one of those (many) switches where a tired original is better than a new replacement. Some find it worthwhile to use the switch to activate a relay to turn on the actual brake lights.
David "not gotten around to that yet..." Lieb
David Lieb

Thanks Bill, David, et all.

Put the two wires together to bypass the switch, and bingo! the stop lights came on.

So switch it is! Perhaps it's a bit much to expect a switch to last more than a couple of years these days.

The little actuator pin moves in and out ok with good spring pressure, so must be the contacts within.

David, if you have a good OE switch that's surplus to requirements, I would be very grateful.

Dave
Penwithian

The new switches cant handle the current and two years is good for one. You can fit a relay to get over the problem
Alex Sturgeon

fitting a relay is "de rigeur" these days...

I'm glad that was ALL it was, visions of you working your way back from the lights looking for open circuits

:-)
Bill sdgpm

will see if I can lay hands on it, but am on hols for a week from Sat morning so a bit busy Friday....
David Smith

For information 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: http://homepages.donobi.net/sufuelpumps/
Cheers - Dave
David DuBois

Dave I've found it, can you email me please, davidDOTsmithATstonesDOTcom
David Smith

This thread was discussed between 28/04/2009 and 01/05/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.