I have motorcycle trailer with a small breaker box which feeds two overhead flourescent lights, two exterior halogen lights and 3 interior outlets. The box has room for two breaker, but currently only using one, 15-amp breaker. When I connect plug into my garage's non-GFI outlet I have power. When I plug into my outside GFI outlet, the GFI outlet pops. It pops even with all connections disconnected. I can only get it to not pop when I remove the wiring from the incoming extenions cord to the hot, neutral and ground. If I have any of the incoming extension cord wires connected to the break box, the GFI pops. Is the breaker box - small with just room for two breakers - somehow bad? Is their something else I should be looking at? It does not add up to me that even with all the wiring inside the trailer disconnected, the GFI will still pop... Any help is much appreciated, thanks!