side lights and MOT

Swap bulbs from side to side. If the dim one moves to the other side check bulb wattage and replace as necessary. When bulbs get old the glass can get discoloured. If the fault stays put, then you have a wiring problem. with the lights on, measure the voltage on each side of the bulb with respect to the battery terminals this will tell you which part of the circuit is dropping the volts. Replace wiring, fuses switches as necessary until you get virtually full battery volts at the bulb

hth

Bob

Thanks to all replies it was the bulb, black and burnt after only `14 months. A halfords own brand, will buy from France next time Thanks again