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MG MGB Technical - Access to Brake Switch

I have a 1969 MGB. The brake lights do not work. The manuals that I have do not provide information about how to access the switch. Any information regarding access to this witch will be appeciated.

Thanks in advance

Tom

tomt852@sbcglobal.net
TPT Turton

Tom - Early MGBs have a hydraulic brake light switch that is screwed into a 4 or 5 way adapter that is on the front, right inner fender just below the voltage regulator. Later MGBs use a mechanical switch mounted on the brake/clutch pedal box. I am not sure where your car falls in the change over, but those are the only two places where the switches are found. The hydraulic switch will have a green wire and a green/purple wire attached to it. The mechanical switch will have two green pig tail wires attached to it that in turn attach to a green and green/purple wires.

Be aware that replacement brake light switches (with the exception of the hydraulic switch sold by the Ron Francis Wiring company http://www.ronfrancis.com/ ) are rather wimpy switches that tend to fail in a short period of time. You can make and install a relay.arc suppression circuit at the same time you replace the switch that will cure the problem. For information on making and installing the circuit, see the article, Brake Light Relay in the Other Tech Articles section of my Homepage at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

To add to what David says, I believe a 69 will be the later style.

Charley
C R Huff

Tom

If you have the switch mounted on the clutch/brake cover I think the 69 does), prior to taking it out and replacing it, try screwing in in a turn or two. These switches have a tendency to vibrate out and it just takes a little outward movement for the contact to be lost with the break pedal shaft. This is a common issue with these systems.

Bruce Cunha

Tom

If you have the switch mounted on the clutch/brake cover (I think the 69 does), prior to taking it out and replacing it, try screwing in in a turn or two. These switches have a tendency to vibrate out and it just takes a little outward movement for the contact to be lost with the break pedal shaft. This is a common issue with these systems.

Bruce Cunha

Bruce - "These switches have a tendency to vibrate out and it just takes a little outward movement for the contact to be lost with the break pedal shaft."

If that happens, the brake lights will come on anytime the ignition is on. The plunger in the switch is pushed in by the brake pedal to turn the brake lights off. When the brake pedal is depressed to put the brakes on, the plunger is allowed to push out (by spring action within the switch), thereby closing the contacts and turning the brake lights on.

Tom - When you remove the switch, check to see if the plunger moves in and out freely (they periodically get gummed up and won't move freely). If it doesn't, use some spray cleaner (I use BrakeClean) to see if you can get the switch working correctly. Cheers - Dave
David DuBois

Tom,
there's a recent John Twist video that may also help you
Nigel Atkins

FWIW North America got the mechanical switch on the pedal box with the Mk2 i.e. in 67, UK cars not until rubber bumpers. On my V8 only one and a half turns is needed to move the switch from just failing to turn the lights off, to just starting to reduce pedal free play. It's important not to screw the switch in too far, which holds the pedal partially operated, or the bypass port in the master can be blocked which causes the brakes to stick on as the fluid heats up.
Paul Hunt

This thread was discussed between 02/06/2013 and 03/06/2013

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