I should probably ask this in another forum, but I'll try here first. I'm having trouble with the Humminbird 858 depthfinder shooting to 70-100 feet whenever I turn on the trolling motor. It works perfectly when trolling motor isn't running. I thought that it might be vibrations from trolling motor, so I wrap the clamps with rubber hoses and it still does it. Could it be interference with the power wires to trolling motor? Or could it be my transducer. It's brand new.

It sounds like electrical interference to me. Where do your wires run from the Bird? Are they connected to the console or all the way back to the cranking battery?

Bogey...Not sure. I bought the boat (Legend bass boat) brand new and that depthfinder is what I ordered with it. It hasn't worked from day 1, but I don't want to take it in and miss prime fishing time. I thought that it might be a quick fix that I might be able to do.

I would start with the wiring. Find out where the wires are ran and go from there. I am also assuming that you have an external transducer. Most likely, that will not be your problem. It is most likely a wiring issue that causes interference when both of the devices are used.

Do you have any other forms of communication(from the 858)? Like an interlink? or an ethernet cable? The reason I ask is that when you disconnect your head unit, there will be 2-3 wires that are connected. Make sure that these are in the setting correctly. Then you can determine the power wire. Follow the power wire to its source and make sure that all connections are secure.

Call Humminbird. They will send you a small choke to wrap onto your transducer cable and your problem should be resolved. You didn't say but I'm willing to bet you have a fortrex trolling motor. This is a very common problem with front mounted units.

I am running the Motor guide 109 trolling motor. I'm thinking Bogey is on to something. I do have it inter linked to a Humminbird 998SI in the dash. Both units have their own transducer and GPS hockey puck. I will check the wiring. Thanks guys for the input.

The motorguide 109 is the same digital trolling motor as the fortrex. What I said still applies the interference is almost definitely coming from your trolling motor. Here is a video of how to install the choke. http://www.youtube.com/watch?v=EM3xNctWaO4