The factory put an inline fuse on the radio circuit. It makes sense to isolate the short circuit away from the main loom, or risk the short to get more complex than you want it because the loom is all tied together. I added an inline fuse to the lamps on the license plate holder just because I imagine them getting smashed being on a hinge and protruding out so much. It is intended to isolate a short so I still have brake lights because those leads, brake, stop, turn, backup are all in the same loom. I wish we had loom lay-out drawings, so much easier to visualize. I've found the blade type fuse holders to be awesome design, but I always have trouble finding them finer wires like 16g. The spring/connectivity for glass-type-inline-fuse-holders isn't the same as the spring on a Toyota fuse block, so yes, I'm suggesting to carry more diverse fuses with you.
I've been tempted to change the plug in the glove box so that it is polarized. Just an ideal, but, it might be more convenient? You could have everything operating smooth and predictable in a familiar kind of way. 12V DC but run on 110V AC wire (which is everywhere, use the kind that are twin cords joined like factory incandescent trouble lamp, not a cord packed in a common insulation). Also, if you look with a magnifying glass, 110V cord is identified with a stripe or some kind of text or whatever, so it could be a great source for 16g or 18g runs to things outside the vehicle, easily added to or shortened with additional links, more compact than using multiple cigarette lighter plug sockets, also better quality, and less expense. I could see a laptop charging in the tent outside the vehicle, or solar controller recharge applications.
The cigarette plug portion on the dash is better for routing wires away from gear shifting, heater functions. The old factory socket isn't smooth on the inside, but, it does make the connection to a USB adapter.
I have a double USB socket simply hardwired into the radio circuit, it rests in the center console or passenger seat rail kinda loose. I might charge a phone(s) if the engine is or isn't on, "acc" position on switch on the column, or I can plug into the factory cigarette lighter if I don't want to have the key in. I kinda like having wire looms run parallel to the rear heater lines; the transmission hump is a mechanical chase of sorts. I even have my reverse lamps switch sub-harness routed here with the rear heater sub-harness, fuel sender lead, and USB power sub-harness to 5V adapter plugs.
I killed an off-grid 12V AGM because the phone's operating system uses tons of power if you have wi-fi on, and I wasn't keeping close attention to the draw. The trickle charger won't deal with a battery that has been run that low. Nice thing about the 40 is it was never in that 12V to complex and electronic 5V USB-band-aid-world.
