just installed one of these , used it thursday on cross lake worked fine. took it to fairhaven today and it doesnt read anything after 81 ft, just blank screen. then it started doing it everywhere at 60 , 50,. i woould bring it up a few ft and it would work. drop it back down and blank , does anyone know whats causing this? it is mounted on the oppostie console as all my eletronics only thing on that side of the boat is a rigger and fm cd player which i never turn on. the power wire is ran to the same fuse box as all my other stuff though then the power goes to the back of the boat to another fuse box that has my riggers on it. this is my first temp down speed device so i really dont know much about them. also the ground wire on the probe is that supposed to go on the rigger cable ? no instructions on what to do with it so i let it just hang. is that right?