Fuse requirements for DF5 Pro

[Jim_MI]

Short version: Fuse to FF is suddenly blowing and I don't know why?

Long version: I wired my SOT fishing kayak with a 5A inline fuse at the +terminal of the12V battery, then to a Blue Sea Systems marine grade 6-circuit fuseblock. I am only energizing 2 circuits, each through individual ATC blade fuses; one for a cigar-lighter style USB charger (to keep cellphone charged out on the water) and one for my DF5-Pro Fish Finder. I used 3A blade fuses for both the USB charging circuit and the FF circuit. The fuse block is in a guaranteed dry location. The battery and various power lines lay in the bottom of the kayak hull and may occasionally get damp but never submerged. The battery-to-fuseblock wire and the power line from fuseblock-to-DF5P use 2-pin Quick Disconnect fittings that are soldered and heat-shrinked for water protection and I only fish fresh water. The battery-to-fuseblock plug is disconnected between outings so I can charge my battery "offline" without affecting peripherals. Everything worked fine for the past 6 months until this morning. I unplugged the battery charger and plugged the battery power line into the fuse block but the DF5P did not fire up. The USB charger was getting power. I checked the fuse block and discovered that the 3A fuse in the DF5P circuit was blown. I replaced with another 3A fuse and that immediately blew. I visually examined all wiring connections and found no faults. Checking with a multimeter, I find proper voltage with no short between the fuseblock and the DF5P quick disconnect plug. When I check continuity across the terminals of the quick disconnect plug going to the DF5P however, there is a "short" detected. But, without knowing the wiring inside the DF5P, I suspect that this is normal. So 2 questions:

Q1: If one checks continuity between the + and - power lines of a DF5P MFD, would it normally show continuity (ring-out as "shorted") or has mine suddenly gone bad for some reason?

Q2: What are the proper fuse requirement for my wiring situation? Review of the manual shows that a 5A inline fuse should be used between the distribution panel and + power line to the DF5P (see pages 23 & 38) but elsewhere the specifications are for 2A slow blow or 3A thermal fuses (pages 39, 132).