The square are just like the round, there should be two nuts on the bracket that holds the gauge into the dash,on my boat you can get to them from the lower ac/dc panel door. if not there should be four screws that hold the gauges panel to the dash and the will lift out all the gauges.Look at the wire colors and mate them the same. I would clean and grease all the connections and it a easy job, what is wrong with the old ones, can't you clean them up?