What was found
THE AFT LIGHT EMERGENCY TEST SWITCH WAS DISCOVERED TO BE INOPERATIVE. THIS IS CONSIDERED TO BE A DEFECT IN THE EMERGENCY ESCAPE SYSTEM AND COULD HAVE AN ADVERSE EFFECT ON THE EVACUATION ROUTE. MAINTENANCE FOUND THE SWITCH CAUSING A FLICKERING OF THE LIGHTS AND APPLIED SECTION 1 OF ER/A 588159-14. IAW B757-300 WDM 33-51-11 THE AFT EMERGENCY LIGHT TEST SWITCH WAS REPLACED. OPERATIONAL CHECK WAS NORMAL. THE AIRCRAFT IS OK FOR SERVICE.