What was found
LAUNCHING ON A SCENE FLIGHT, ON STARTUP THE LANDING LIGHT CB POPPED & WAS RESET ONCE. THE STARTUP WAS COMPLETED. AFTER TAKEOFF THE NURSE SMELLED A BURNT WIRE SMELL & THEN THE REST OF THE CREW CONFIRMED THE SMELL. THE PILOT IMMEDIATELY RETURNED TO BASE APPROX 5 MINUTES INTO CRUISE FLIGHT WITHOUT INCIDENT. THE MECHANIC CHECKED THE ACFT & FOUND THE PATIENT OVERHEAD LIGHTING WOULD NOT COME ON & A BREAKER BEHIND THE LT CREW MEMBER WAS TRIPPED & WOULD NOT RESET WHICH IS ALSO THE AREA FROM WHICH THE SMELL WAS COMING. THE LIGHT WAS DEFERRED & COLLARED FROM MEL LIST BY THE MECHANIC & PUT BACK IN SERVICE. THE MECHANIC INSPECTED THE OVERHEAD CB PANEL & LANDING LIGHT INSTALLATIONS & FOUND THEM TO BE OPERATIONAL & AIRWORTHY. THE LIGHTING POWER SUPPLY LOCATED IN THE MEDICAL SERVICE MODULE WAS THEN FOUND TO BE BAD. IT HAS SINCE BEEN REPLACED & THE DEFERRAL CLEARED.