connect up just the fan motor and see if it trips then just the light wires. That way you can isolate which part is bad. You could have a shorted out light bulb or a wire crushed under something when it was put together or a miswired pull chain switch. A radio shack meter can help you with continuity - you should have none when the light bulbs are removed, light pull chain switch is off or the fan pull chain switch is off.