Faulty Brakelight On Ford Focus

[smartypants10101]

my 2004 ford focus uses the double fillament bulb type for its brakelights, when i press the brake only one side wont light up even tho the tail light still comes on , i have changed the bulb and still no joy , any suggestions ?

[TonyV]

Maybe a bad earth connection do you have access to a multimeter

[smartypants10101]

yes i do have test meter

[bhg481]

If you have a multimeter measure the resistance between one of the lead blobs on the base of the bulb and the metal casing of the bulb. Then measure the other one - they will be different but both should give a reading. If only one gives a reading try another new bulb.
If both give a reading, with the sidelights on CAREFULLY measure the voltage between each pin in the socket and earth. Get someone to press the brake pedal and check the one which was zero - it should be 12V.

[TonyV]

Just basically test circuit

[smartypants10101]

i got a test meter but not that well up on how to use it proper, wander if it could be a faulty microswitch on the brake pedal

[bhg481]

Brake lights are usually wired as a pair, so if one works the other should.
Try a different new bulb or even the one from the side that works.

[bhg481]

Another thought - have you put the bulb in the right way round. The pins on these bulbs are set at different distances from the base; if you force it in the wrong way round one filament might not work.

[TonyV]

Very difficult without eyeballs disconnect the micro switch and buzz all the cables out. It will be something simple

[TonyV]

And perhaps give new bulb a good push