I believe the tube you are talking about is actually a filter and from what I have gathered, does not need to be installed unless you will be running a vhf radio in the boat. At least that is what the guy at lowrance told me. You just need to get to your local hardware store and explain that you need to insert a 3 amp fuse between the hot wire on your power supply and your battery. A wired fuse holder and a couple of the correct size wire connectors should do the job. Not much to it and I'm not exactly an electrical whiz. With that said, I have yet to try mine out but am pretty sure I got it right and hope to find out this week. Just got the wiring ran into the boat a couple of weeks ago but hit another cold front. Good luck!