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MG MGB Technical - Brake Lights Problem...

Hi,

As soon as I turn the ignition key, the brakelights switch on and they don't turn off anymore.

Could this be a problem with the brake light switch ? Did anyone have the same problem ?

Thank you so much for your input.

Regards,

Marc Wantz
Marc Wantz

It would be useful if you gave us the year of your car Marc as the brake light switch arrangement changed throughout the MGB's production run.
Mike

As Mike says, year and market is everything. Early cars had a hydraulically operated switch in a union, with this type it is probably that the terminals of the switch have been pushed together as the usual mode of failure of these is to *fail* to light the lamps.

Later cars have a mechanically operated switch operated from the brake pedal, and with these if they come unscrewed just a little the lights will be on permanently (they are of the normally closed type, operating the switch opens the contacts). These switches can either be in the front of the pedal box for single-circuit and unboosted dual circuit, or in the cabin by the pedal for boosted dual circuit systems. However you have to be careful not to screw them in too far or it prevents the master piston coming back far enough, which can cover the bypass hole into the reservoir, and then fluid expansion will apply the brakes. For the former type at least only one and a half turns is needed to move the switch between taking up all the free play on the one hand, and failing to turn the lights off on the other, so find the point at which the lights just go out, then screw in a further 3/4 turn.
PaulH Solihull

Odds are that it is, indeed, the switch. Adjusting it, on newer cars, or replacing it on earlier cars, is the cure. RAY
rjm RAY

Hi,

First of all, I would like to thank you for your responses - much appreciated.

It is a 77 Rubber Bumper Model, which was converted to a V8 Chrome Model (looks like 1973 MGB), but I think that the brake system is still the original one (I say I guess, because I imported the car last year from the UK). Date of first immatriculation 07/07/1977 (funny date)...

Could this help you ?

Many thanks,

Marc

PS: Below a picture of the car & son... ;-)

Marc Wantz

Hi Marc,

Your brake light switch probably looks like mine and is located on the back of the pedal box:
http://incayellow.com/posts/new-brake-switch
It will either need adjusting (screw it in/out until you get brake lights when you press the pedal and go out when you release it, then tighten the lock nut), or possibly replacing if the plunger has seized.

Adam
A Liptrot

According to Clausager the brake light switch moved from the pedal box in the engine compartment to by the pedal in the cabin in May 1977, so it depends on what you mean by "first immatriculation". If manufacture, then yours should be in the cabin. But if you mean first registration the car could have been built before or after Clausagers date, and could be either. If you have the dual circuit brakes with the integral servo it will be in the cabin. Before that UK cars had the single circuit system with the remote servo, so the switch will be in the engine compartment.

But as it is a conversion none of the above may apply ...

In either case you need to be very careful in adjusting it, as explained earlier. Screw the switch in until the lights just go out, then a further 3/4 turn. I doubt the plunger has seized, that would stop the brake pedal coming back all the way which could cause the brakes to lock on, unless a PO had deliberately unscrewed the switch a bit to stop that happening instead of replacing it.

PaulH Solihull

This thread was discussed between 25/07/2010 and 27/07/2010

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