I've got a 99 (T) 1.3 GX, I presume this is a K11!
Anyway, for some reason, when the brake is pressed in the car, the side lights come on at the same time!
So, I've had a look at it. I've narrowed it down to the left hand side bulb holder (i.e. the bit which holds the 3 bulbs).
I did this...