Ford Focus Mk1 brake light staying on?

[David]

it sounds like a bad earth, have you or any one else replaced a rear bulb recently? i have came across this before and someone had fitted the wrong type of bulbs to the o/s/r tail lamp unit, the contacts bridge the conectors on the lamp unit and send the circuit to other lamps, i would check this as it gives the impression of a bad earth

hope this is of some help

 

[postie_uk]

the brake lights work normally until the side lights are switched on then then the brake lights come on with them. Have topped up brake fluid which was low.