What could cause brake lights to work every now and then

Replace the right rear brake light bulb. It is possible that the filament has burnt out and has fallen across to rest on the brake light filament. This would cause the condition you are experiencing.

When I had that problem with the emergency light it was the sensor for emergency brake
The abs and brakes sounds like you are loosing pressure in the system

A bad ground will cause the lights not to work. Check the grounds to the offending lights

Light gets power from brake light switch/.May be switch got shorted an brake light getting non-stop power causing it not to turn OFF brake light.

Get the brake light switch checked. Check volt at brake light switch.

It can be faulty brake light switch causing the problem or its wiring short for switch.

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To trouble shoot brake related problem, check the help links mentioned below:-----

Click the link:----

1996 Buick Regal Grand Sport Brake light Switch Location?

http://schematicsdiagram.blogspot.in/2012/04/1996-buick-regal-gran-sport-brake-light.html

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No brake lights on Buick?

http://schematicsdiagram.blogspot.in/2012/04/no-brake-lights-on-buick.html

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Brake lights not working on 1989 BUICK REGAL?

http://schematicsdiagram.blogspot.in/2012/04/brake-lights-not-working-on-1989-buick.html

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How to replace Brake light switch on Chevrolet Tahoe?

http://technoanswers.blogspot.in/2012/02/how-to-replace-brake-light-switch-on.html

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How to replace Parking, turn, and Brake Lights on car?

http://schematicsdiagram.blogspot.com/2011/06/how-to-replace-parking-turn-and-brake.html

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Upper brake lights work, but low brake light not working?

http://schematicsdiagram.blogspot.com/2011/12/upper-brake-lights-workbut-low.html

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1997 Cadillac Catera: How to replace Brake Light Switch?

http://howtobyme.blogspot.in/2012/06/1997-cadillac-catera-how-to-replace.html

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1996 Chrysler LHS brake light circuit wiring diagram?

http://technoanswers.blogspot.in/2012/02/1996-chrysler-lhs-brake-light-circuit.html

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How to replace rear Brake lights on 2004 Toyota RAV4?

http://schematicsdiagram.blogspot.in/2012/02/how-to-replace-rear-brake-lights-on.html

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One brake light on driver side not working, but other lights work?

http://schematicsdiagram.blogspot.com/2011/12/one-brake-light-on-driver-side-not.html

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2002 Lincoln Town car Fuse Box

http://schematicsdiagram.blogspot.com/2012/11/2002-lincoln-town-car-fuse-box.html

2007 KIA Rio: Brake Light Fuse Box Diagram?

http://repairhelpcenter.blogspot.in/2012/06/2007-kia-rio-brake-light-fuse-box.html

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Overhead Brake lights not working on 1999 GMC Sierra 4x4?

http://technoanswers.blogspot.in/2012/03/overhead-brake-lights-not-working-on.html

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Brake lights not working

http://schematicsdiagram.blogspot.com/2012/11/brake-lights-not-working.html

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2004 Ford Mustang: Brake light Fuse Location?

http://howtobyme.blogspot.in/2012/05/2004-ford-mustang-brake-light-fuse.html

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These will help.

Thanks.

OK, the brake light is caused most likely by the emergency brake cable being broken, and the pedal or brake lever is not in position.

Also, the brake light could be caused by low brake fluid level. Check that, too.

Battery light, is caused by the charging system not working, like a bad alternator or shorted out battery, or both.

I would have these issues repaired before driving any distance.

If there is no voltage at the brake light bulb socket, check the brake pedal switch.

Typically, worn brake pads won't cause the warning light to come on. Some vehicles have a brake fluid sensor that can cause the light to come on. Also make sure the parking brake is completely releasing and if you have ABS, make sure everything is working there.
Uneven brake pressure will certainly cause the brake light to come on, that's when the master cylinder is working a lot harder for one circuit (front or back) than it is for the other, indicating either low brake fluid level or damaged/worn wheel cylinders.
If you can't find anything by examining the brakes, you may need to pay for a scan of the ABS computer.

take another look at the switch ? it should be adjustable? disconnect the wires from switch then screw switch inwards towards pedal till plunger is pushed fully into switch? then reconnewct wires and try brake lights work correctly ?

Brake light switch, located on upper brake pedal should be checked, that is most likely your brake light issue, but U say tail lights aren't working, but running lights do, tail lights and running lights I would consider to be the same, so can u clarify that for me? Let me know how the u do w/ brake light switch, and if u have issue w/ tail lights?

back feed causing the brake light to ground off of the head lights caused by bad ground or possible short