Did toliver ever learn how to remove the sender?
That flange should spin off the threads and then the sender can be lifted out. The paddle wheel will be part of the removable section. Obviously, if this is done in the water, you need a blank or other device to stop the water from flooding in.
If you spin the paddlewheel, and nothing happens at the display there is something wrong in the wiring or with the sender itself. The paddlewheel works like a magneto in that as it spins it creates a small current. As it spins faster it creates more current. The display converts the amount of current into a reading in knots. The senders are replaceable but that one looks to be pretty old. If the reading is off by a small amount, 1 or 2 knots, there is a procedure to re-calibrate the display. So, there is a range you can set the speed to and it is a little arbitrary. To paraphrase an old movie, you should set the highest speed to "11" - because it is one faster then "10".
