You have to go to the trim programming mode and check the Multi Function window on your dash. It is the window the Voltage is shown in. When you are i Trim Programming, the one side will remain solid (programmed setting) while the other side will or should move from the sender. If it is the sender, it probably will not move. It is usually a faulty sender, especially if it is Mercury. Once replaced you have Mercury as the default setting, or you can program your own settings. The PDF of the Manual is on line in the drop down menus on the BassCat.com Home Page. BCB