For all of my electronics, VHF, GPS, 2 fish finders, AM/FM/Cassette, accessory plug, etc., I put in a fuse box because there never was one on the boat. This way you have only two or three wires at each terminal on your battery, not the 8 I had when I got the boat.

I forget the size of the wire I ran to the fuse box, but it is about 1/4" in diameter, pretty heavy stuff, but it was recommended by the instructions.

This makes adding new accessories or chasing down electrical problems quick and easy, and fuses are all in th same spot, just like your vehicle.. 12 volt wiring is simple, but study up a bit if you have fancy wiring, and don't just rip everything out, then try to fix it.

Send the fishfinder back, get the warranty work done, get a marine grade fuse box, place the fuse box out of the weather, accessible, but out of harms way, and start over.

I can take a picture and post it if you need help.

One other note, whenever you buy screws, go stainless or silicon bronze.

Andy