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MG MGB Technical - Stop Light Switch

I have a 1971 BGT which was rebuilt about 12 months ago. My problem is that it seems to take excessive pressure on the brake pedal to activate the stop lights. I found the pressure switch on the 4-way junction, but there doesn't seem to be any adjustment. Is this just VERY tight or do I have to renew the switch. A during the rebuild, we used completely new brake pipes and fittings. I'd be grateful for any advice. Many thanks.
Vic Synott

I have a similar problem with my 73 BGT. The original switch activated the lights easily, but a couple of years ago I had to replace the switch and since then I've noticed that the lights don't go on during very gentle braking. So if anyone has the answer I'd be glad to hear it too.
Miles Banister

I had the same thing on my '66 GT, solved by replacing the switch at the 4-way union. There is no adjustment possible. The lights still don't come on until a reasonable amount of effort is put on the pedal, but then nor do the brakes!

Tim.
Tim Jenner

Vic,
If I remember correctly the switch that activates the stop lights is on the petal cover. Also, I think screwing it in makes the petal activate it sooner. Paul
Paul S. Canup

Thanks Paul, but my '71 has the switch on a 4-way which is bolted to the r/h inner wing. Pre 71 was on the pedal cover...those ones can be adjusted as far as I know, but the type I have can't be adjusted or repaired apparently. Back to the toolkit and bleeding the brakes again!

Thanks to all who responded, as usual my two second enquiry turns into another project! Still, at least it's not a eurobox:-)
Vic Synott

Paul,

Depends on the year of car. Earlier cars had a hydraulic switch mounted on a 4-way union under the bonnet, later cars had a normal push switch as you describe. I don't know the date of the change, and I expect some cars have been converted from one switch to another!

Tim.
Tim Jenner

Vic,

I couldn't shift my switch so took it to my local mechanic (who changed it for free). He used a massive pair of mole grips and was much more forceful with it than I was willing to be, but he managed to change the switch without losing any brake fluid or needing a bleed. He just put his finger over the hole and changed the switch quickly!

Tim.
Tim Jenner

Tim thanks for your response, do you by any slim chance, have the part number for the switch. It's mentioned in several books and on the net, as being in existance, but none tells me what to do about replacing it. Thanks to this board, I've now got a pretty good idea, but it was pretty worrying to see the other pipes moving - so far I haven't had the bottle to try to move it with the mole grips. I HAVE to avoid having to replace the pipework too.

BTW - post above should read "post-71" models. One day I'll pass elementary school!
Vic Synott

Vic,

I'll try to have a look when I get home tonight. I was worried about the pipes moving too, actually the mechanic used 2 pairs of mole grips. One held the 4 way union still and the other shifted the pressure switch. I stood back and shut my eyes! :)

Tim.
Tim Jenner

These switches are not made as well as the originals were and it is very common for the point at which they contact to change so too much pressure is required. The switch can be changed quite successfully without having to bleed the brakes. Screw the old one out and screw the new one in - simple as that. Just don't touch the pedal while the switch is unscrewed. New switches are available at all MGB suppliers.

Mike
Mike Howlett

Vic, I have another item for you to check which was the problem on my car. I had the exact same symptoms as you have described on my 73 MGB. I would have to about put the brake pedal through the floor to get the lights to come on, even with a new switch. The problem turned out not to be the switch at all. Check the brake pedal where the switch comes in contact with the pedal by the brake master cylinder. As it turns out on my car, the metal pedal was worn where the switch comes in contact with it. I would press the brake pedal and the switch was actually sliding to the side of the metal brake pedal instead being depressed, and until there was a lot of friction and pressure from me pressing the brake pedal, the switch was not being compressed to activate the brake lights. The metal pedal should be a flat surface where it contacts the switch and there should not be any radii on either side of the metal pedal. Any radii will let the switch slide to the side of the metal pedal instead of being depressed and activating the brake lights. I had remove my brake pedal have my it welded at that point and then I ground it flat like it was suppose to be and I have not had any more problems. If you would like more details, please feel free to email me and I will help you. Good luck.
Robert Browning

Vic,

I bought my switch from the MGOC, part number C16062 (equivalent C16062A) and it was described as "Switch-Brake Light hydraulic". It cost £5.50 when I bought it in 2001.

HTH!

Tim.
Tim Jenner

Robert - you have the post-71 mechanical switch. Vic has the earlier hydraulic switch.


Vic - Check the MGA archives. Somewhere there is a thread on replacing the hydraulic switch with a mechanical one under the dash using readily available replacement. If/when you remove your existing switch note what Tim said about the use of TWO pairs of pliers (mole grips). If you don't hold on to the 4-way union you will probably crimp your brake lines.


Larry
Larry Hallanger

I would suggest bleeding the brakes BEFORE and after replacing the switch. Air in the lines will compress, delaying the point at which the hydraulic pressure switch can activate. I learnt this after changing my switch to no avail. A really thorough brake bleed using a pressure set up got the lights on at the lightest pedal press.
Steve Postins

Job done and everything hunky-dory. Changing the switch was very easy in the end. Screw out, screw in, quick bleed all round just to be on the safe side and that's it! No more near tail-end blushes. Endless thanks to those who helped. I'm very grateful.
Vic Synott

This thread was discussed between 18/06/2003 and 20/06/2003

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