I have twin 502 mpi engines which I took out to tidy up the bilge. After reinstalling the Port engine I tried to start the engine before installing the Starboard engine. When I turn the key switch I have no power to the gauges and nothing to the engine. I turned the key switch for the engine that is not yet installed and I have power to the gauges. I double checked to make sure I had the correct harness plugged and it is impossible to switch them. Both engines ran fine before I removed them. Is it possible that both engine harnesses have to be connected or could I have a faulty kill switch