I have a Humminbird 200DX fish/depth finder. Current tranducer works great showing fish, depth, and water temp. Speed displays 0 mph as there is no speed sensor hooked up. I am looking to add a speed sensor, but do not know what part number is needed. I went to Humminbird website but since the 200DX is an older unit, it is not mentioned much there. I did find 2 speed sensors, 1 speed only, 1 speed and temp. My current transducer appearently determins the water temp as it is displayed on the screen, but not sure if that needs to be removed to install a speed sensor. Does anyone know what speed sensor is needed, speed only or speed/temp and what part number / where to buy? Thanks a lot. Funny had boat 5 yrs and now looking to see mph....