When the wiring box dedicated for splicing transducer cables arrived I spent half a day hanging down into the aircon space splicing small cables.

I had no idea a broken transducer cable could be fixed although there´s still a debate ongoing out there. Using a dedicated wiring box for splicing transducer cables is well recognised by Garmin but not by Raymarine. 

Once the box was installed I tried the Raymarine DSM-300 and to my joy it was working !

There are videos out there showing cable splicing but none about this wiring box. Fortunately there´s a good manual enclosed in the package with very clear instructions.