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Testing speedometer transducer.

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  • Testing speedometer transducer.

    I have two transducers and cannot tell which one does the speedo. Someone unmounted them and just let them drape into the boat. I want to test them somehow and see which one is for the speedo. Any ideas?

    Right now the speedo does not work.

    Lastly, if I detemine the transducers are bad and cabling, can I just buy any transducer or does it have to be perfectly for the speedo head?
    1988 Four Winns Sundowner 235, 5.7-4V 260HP OMC Cobra


  • #2
    Re: Testing speedometer transducer.

    On my setup the speedo is connected to a Pitot Tube. A tube runs from the speedo to the back of the boat and connects to a pitot tube assembly that sents air pressure to the speedo.

    http://www.iboats.com/Teleflex-Pitot...-view_id.40246
    1994 19' Chaparral 1930SST Bowrider 5.7L 4bbl Rochester

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    • #3
      Re: Testing speedometer transducer.

      On my bayliner I bleive I have one too. But my sea ray have a black box with a wire coming out of it. One is for a fish finder and one is for the speedo. I am very unfamiliar with these setups.
      1988 Four Winns Sundowner 235, 5.7-4V 260HP OMC Cobra

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      • #4
        Re: Testing speedometer transducer.

        Originally posted by Fordiesel69 View Post
        I have two transducers and cannot tell which one does the speedo. Someone unmounted them and just let them drape into the boat. I want to test them somehow and see which one is for the speedo. Any ideas?

        Right now the speedo does not work.
        What speedo are you referring to? Dash mounted or fishfinder display?

        A transducer will not give you a speed indication. You need either a speed wheel connected to the fishfinder (if you have that option) or a pitot tube mounted on the transom and connected to your dash speedometer.

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        • #5
          Re: Testing speedometer transducer.

          You either have a pitot style pickup (has a plastic tube connected to it and is not electrical) or you have a paddle wheel style (electrical). It is very obvious as to which type you have. If you still can't tell, stick your head under the helm and look at the back of the speedo. It should have only two wires on it for a light and the actual "business" connection will be a small plastic tube that simply slips over a fitting. If the speedometer is electric it will have three more more "electrical" connections. Very few speedometers are electrical so what you are looking at is very likely a pitot and a fish finder transducer (which has nothing to do with the speedo).

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          • #6
            Re: Testing speedometer transducer.

            I feel like an idiot now. The small grey tube half way down the outside of the transome is not a vent tube like I thought. It is the tubing for the speedo. It is broke and the space where the pitot tube was no longer has the pitot attached. So now all I have to do is buy that and splice it together. As for those 2 transducer boxes, I cut the off as they belonged to fish finders that are no longer on the boat, and who knows where they are.
            1988 Four Winns Sundowner 235, 5.7-4V 260HP OMC Cobra

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