Any other electrical faults? any aftermarket electrical equipment been fitted about the same time as the light problems?(phone chargers, Sat nav',  etc.-remove temporarily to make sure they are not interfering with operation of electrics) are you sure all the bulbs fitted are the correct type - a twin filament bulb fitted where a single should be perhaps? maybe remove any bulbs fitted recently and see what happens. poor battery condition/low voltage/dirty connections at battery or earth wires can cause electrical problems like this. give more details of vehicle - year, model, spec etc. and say if problem is intermittent or every time you use the brake +/or the indicator. if you have a tow bar and trailer light socket fitted to it water entry into the socket could be the problem.