I know the interference issue has been talked about many times before but mine seems to be different this time. Run humminbirds front and rear. The boat had a 24v motorguide and I got interference on the front graph when running the trolling motor. Before I tried any of the suggestions to take care of it, I bought a 36v terrova. No more interference. Traded the 36v for a 24v terrova and took it out for the first time today. I was using the built in US2 transducer and every time that I turned it on, I lost the bottom reading and the screen just filled with interference. Units are linked together so I switched it back to the transom transducer and same thing. Later in the day I was in the back of the boat and found that it was also getting the same issue on 2d,di and si screens. It was running everything off of the rear transducer. I never had the trolling motor effect both units.

Trolling motor has it's own batteries and the cable runs on the left side. FF both wired direct to the cranking battery and the wires run the other side. Units are linked together along with the MK link through a 5 port hub. Is it common for the trolling motor to effect both units? It never has before for me.

Both of mine were effected through the network. Check the fuse in the trolling motor head and see if it is blown. Could be an issue with prop or motor. One thing that fixed mine was the $65 choke that Humminbird makes.

Ok thx. I didn't know if it was common for both to be effected. I forgot about the fuse and then will look at the choke. Thanks.

If you haven't done so, you may want to also look to see if you are using a Ferrite Ring. They are basically used to reduce high frequency noise that can be product by motors - especially trolling motors. You want to add it to the power connectors.

Ferrite Rings on ESC�s: What Do They Do and How Can You Use Them?

Haven't used the fish finder in a while and finally tried it out today. I went to radio shack and bought some snap on ferrite rings. They were $5 for a bag of two. I snapped a couple on the trolling motor power cable and the cables on the ff. It fixed the problem. Just wanted to post an update so people would know that there is a cheaper solution that can work.

That's great you got it resolved with just those. I have six of them plus a ferrite ring on the transducer cable, plus a TMC-1 on the trolling motor power cord and some grounding wires and still get RFI on 800 kHz Imaging.
Replaced the motor lower unit also on my Motor Guide Tour. Makes no difference if I use a dedicated electronics battery or the starting battery.

Wayne have you tried disconnecting anyone negative cable from your on board charger to the trolling battery/s

No, since I don't use an on board charger connected to my starting battery or extra battery to run my electronics. I get the RFI using either battery.
I use the extra battery when fishing electric-only waters.

With my Helix 12 CHIRP SI GPS, I was not getting RFI at first, then after installing the first software update, I get RFI on 800 kHz SI. It's really no bother though since I don't use 800 kHz. I just mess with it occasionally to see if I can solve it.

Just ordered a couple of Mix 43 ferrite rings last night to try.