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MG MGB Technical - Brake Light Switch

I changed my master cylinder in my 74.5 MGBGT. When all put back together I experienced problems with my brake lights; staying on then not going on at all. I have adjusted the switch several times and set at several distances but now I have no brake lights. What am I missing here? Get a new brake light switch or....? Thanks, JOHN
JW Colson

Remove the switch drom the cover and operate the plunger by hand. If the brake lights work with every stroke you have an adjustment problem, if they don't, order a new switch.
John H

Wouldn't think that changing out you M/C would cause your brake switch any harm. Experience suggests that such things usually result from either improper adjustment or a bad connection (missed connection).

Have you pulled yours and tested it? If I remember correctly (it's been years), circuit is on with ball plunger out and off with plunger pressed in. That is (assuming all else is correct), if switch is screwed out - brake lights should come on (test). If working, then screw in until brake lights go off and tighten lock nut. Again - if my memory is correct - might have it ass-backwards. Course, one should check for 12 V to the switch at the start - should have 12 V at green wire from fuse box. Thinking, another check might be to disconnect switch and jumper the two lead wires to switch and see if brake lights come on.

Steve Buchina

Not sure if this is the same setup as a 68B or not, but I had the same problem and found out there was a difference in the spacers for the pedal shaft and when I re-assembled after master cylinder rebuilds, my brake pedal did not contact the switch. I placed the spacers and pedals back in the correct positions, and everything worked. That was a newbie moment. Anyhow hope this helps.

Edward Bullard

John - There are good suggestions above, particularly Edwards regarding the pedal/spacer positions. After exhausting everything else, if you find that the switch is bad and you have to get a replacement, be aware that all the replacements available today are extremely light duty and will fail after a short period of time (I had one fail after only two weeks) due to the contacts burning. You can make the replacement switch work for many years by installing a relay/arc suppression circuit. Instructions for making and installint this circuit are available at:
Cheers - Dave
David DuBois

The comments have been helpful. My switch appears out. Now, Where can I get a new switch which is not light wieght and without having to construct a relay? Thanks, guys.
JW Colson

John - I don't know of anyplace that carries a switch that is heavy duty, but someone on the board may know. There is really nothing to putting together a relay/arc suppression circuit and it will make even the light duty switches that are readily available last a lifetime. Cheers - Dave
David DuBois

This thread was discussed between 07/05/2007 and 09/05/2007

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