Renault Megane Faulty Lighting?

I have a '96 Renault Megane 1.4RT, when I apply the foot brake while driving or when idling, it interferes with the fog lights and the indicator lights. When I apply the foot brake the fog light illuminates also, both in the rear light (left hand side only) and also on the indicator panel on the dash. When I apply the foot brake while indicating left, the indicator light will either indicate faster or stop altogether. I assume it has something to do with some possible electrical crossover of the wiring - anyone got any idea??