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MG MGB Technical - Brake lights on ALL the time

When the ignition is on, but not the engine, the tale lights and all the lights work fine, brake pedal activates brake lights, you know. When the engine is running though the brake lights WONT turn off... not the tales, but the actual brighter brake lights, any ideas?
Bryan Corey

Bryan: You come up with some posers alright! I can't see how having the engine running would make any difference, even if wires were crossed somewhere. Are you absolutely sure that the brake lights work normally with only the key on? I had a well worn switch that would work fine one time (i.e brakes lights off when pedal released), then stick on next time. The solution was a new switch.
Possibly you have a grounding problem. Check the 'Electrical Help" section on this forum and read about errant circuits. The license plate bolt (left side looking from the rear) is a major grounding point for the fuel pump and the lights in the tail end of the car. Maybe the circuits are grounding themselves through the brakes lights. Seems like the a long shot tho'. Check the green and purple wires for cross connections.
Andrew Blackley

Ill check the electical area, but I swear, works 100% PERFECT with just the key on, but as soon as the engines on, whabam, so are the brake lights.
Bryan Corey

Ok Bryan I am going to take a flyer at this…have you a servo? If so is it working correctly? It could be that when the engine is running, and thereby activating the servo, and in turn activating the brakes. I know that switch is activated via the pressure in the brake system, rather than the usual way of pressing on the brake pedal. BTW I have just thought maybe if your getting white smoke out of the exhaust, as per you other thread, then it could mean that brake fluid is burning off. The only way it can get into the engine is via a faulty servo…maybe, just maybe it is all fitting together. Look at the level of you brake fluid regularly to see if it is disappearing.
Cecil Kimber

Bryan,

Had the same problem awhile back with my car. It turned out to be the brake light switch. On my car it is mounted on the master cylinder cover. If the switch is not making contact with the petal lever or the switch is bad the lights will always be on.

Hope that helps.

Rick
Rick Bartell

I guess Im just dumb, it was the switch, we had the cover off the brake/clutch fluid area and never screwed it back on because of stripped screws.. I fitted the cover correctly and screwed it in with new screws and the tails work fine now, thanks all!
Bryan Corey

This thread was discussed between 20/06/2002 and 22/06/2002

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