p38 autostuck in low range

Hi , my p38 has put itself in low range . I ve been told it could be transfer box hi/lo motor , so i scrounged one off a mate - when i removed it from his spare box the arrow shaped shaft was pointing towards drivers side and when i removed mine it was pointing down .If i try to turn mine with a spanner it spring back to pointing down , so i cant get motor on . What am i doing wrong ? Am i an idiot ? HELP !