I recently purchased a boat with a 90hp mariner outboard. I am not sure of the year of the engine, however I do know the boat is a 79. If I had to guess I would say that the engine is not the original.(looks to be maybe mid to late 80's. My question is this.. The boat has a speedometer and all apears to be hooked up except for a thin black tube which runs to the back of the boat then just stops there(it looks like maybe it was just cut off there. What is this hose and where does it go hooked up. when I blow on the hose the speedometer does move slightly. Thank you for any help on this.