Use about 3 meters og awg 5 (16mm^2), and then Connection to the TM with Anderson plugs, and everything is soldered on properly.
I could trim the cables down to something like 1-1½ meters,

I have the exact same setup HDS9 & xi5 saltwater with no issues. Its always possible you have a faulty T connector or terminator or cable.
I would start by replacing parts on the NMEA cabling (terminators or T's or cables) would be nice if you had a fishing buddy you could borrow parts from to troubleshoot,
or spend the $$ to get another complete set and see if the problem goes away.
something is definitely misbehaving or faulty

good luck, i like your tidy box.

Another try: you have connected your pinpoint with a long cable to the top of a t-connector.

As far as I know, you should put your cable between two t-connectors and place the last t-connector in the front of your boat, so that you can connect your pinpoint cable direct to the top of a t-connector. I hope, you can understand this?

Other: your network extension cable should be placed between two t-connectors, not between t-connector and pinpoint cable.
I made my setup this way (as it is written in the manual), but I have not been on the water since that Installation.

Thanks guyes, ill let you know when i figure something out.

First off ill try to cut the cables from battery to TM, down, and make a proper ground connection with a cable to the head of the TM, and if that doesn't work, i'll have to get a hold of some of the dealers where i bought the items :)

Hubert@ i have tried to rewire the NMEA network with the long cable in the backbone, and its still the same.

I don't know if Xi5 has this but Minn Kota does. In the head of the TM there is a fuse connected with a grounding wire (and I guess that again grounds the engine itself). If that fuse breaks, all hell is loose with interference.
One way to break it is to charge the battery to the TM with the TM connected. Not saying this is your problem, but could be worth looking into.

Team Colibri wrote: What?
*make big eyes*
The Fuse in the MinnKota TM gets damaged if you charge the battery while the TM is "shut off" and only connected?

That can happen. :) Always disconnect the TM when charging the batteries, regardless of brand.

So tried to make the ground connection and trim the power supply cable down to 2 feets, Just used tape to ad the ground connection, to the head of the trolling motor.

But its just the same as before. :/

Here a picture of the set up without the NMEA or ground connected, the white wire was the ground connection.

Would it make sense to make a common ground from the - of the 12v sonar battery, to the 1 of the 24v TM battery ?

No, that would not make sense. :) What is the white/ grey cable on the right battery?

The white wire, is Connected to the negative of the 24v system, and was the one I used to try to get a propper ground, from the head of the trolling motor,

Found This diagram on google, and they seem to use a common ground from the 12v to the 24v system, but they also have som other components.

www.lindamaki.com/wp-content/uploads/201...r-wiring-diagram.gif

Here is a better picture of the entire set up.