Just an update, I've managed to fix by setting the default aircraft of P3D to the Captain Sim 777 with the GEN's switched on. I'm not too pleased with this method but it does work.

The reason that the landing lights don't work is that when loading into the aircraft the GEN's are switched off. Not sure why this happens, I wish there was a way to load into it when the engine fully running with the overhead fully working.