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MG MGF Technical - Brake Light Switch !!

Hi.... I have discovered that my brake lights are beginning to jam on. A dab of the brake pedal sometimes cures it, but its very intermittent. Can happen all day or wont happen for days. Ive had a look under the dash behind the pedals for an adjusting plunger switch but the F set up looks as though its a sealed unit and cannot be adjusted.
My question is........... can an adjustment be made?...if not how much is a new switch and how easy to change it ?
D Jamieson

Lots of discussion on this in the archives but it is likely that the brake light switch piston has been pushed inside the cylinder. Remove the switch from behind the Brake pedal, it just twists to one side and pulls out. Remove the electric connection and then carefully extract yourself from the precarious position you have got yourself into, upside down under the steering column.

Once the switch is removed give the piston a hard pull outwards and it should come out from the cylinder, then just replace and all should be ok.

If you have no play in the cylinder then the switch could be worn and you will need to purchase a new one.

Hope this is all it turns out to be.

If it doesn't "fix" by pulling it out, some others (me incuded) have screwed a screw + a washer into the end of the plunger which changes the position the switch activates to some success.

As Chris says: lots in the archives! And if all else fails there's a Mk2 switch that doesn't have the adjustable plunger (apparently!)


I bought a mk2 switch when my brake lights started playing up.

Put my back out getting under the steering wheel to get at the switch, removed the switch and released it anyway.

Then looked at the mk2 and found that it didn't simply clip in place like the mk1 but had a threared shaft and retaining nut.

As it took all my effort to get the mk1 out I thought that there was zero hope of my getting both hands and a spanner down there to fit the mk2.

Mk1 has been perfect since the BBS inspired "overhaul" and I am saving the mk2 until I can convince an MGR dealer to hurt their back under warranty.

Until then it can sit in the tool box.

Was the BBS "overhaul" the pulling the plunger out overhaul :-) ?
D Jamieson


Switch has an internal 'ratchet-like' self adjustment mechanism and the position of the brake pedal 'at rest' sets the activation point.

There are theories as to why it becomes hyper sensitive over time, i tend to subscribe to the 'accidental lifting of the brake pedal' one as this will adjust the mechanism inside the switch and is very easily done whilst getting in and/or out of the driver's seat due to the low position of the steering wheel.

The only thing i have to add to the above instructions is that you need to keep the brake pedal depressed whilst you are re-inserting the (extended) switch and then gently release the pedal afterward so that it finds it's own 'at rest' position, thus re-adjusting the switch.

Scarlet Fever

2be underlined.
The second reason is settling of the sheet metal work over the time from more or less hard braking. The harder you brake the earlier the ratchet needs to be reset, once.

Ladies and Gentleman, control you feet !!
Dieter K.

This thread was discussed between 21/12/2002 and 22/12/2002

MG MGF Technical index

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