So I am pretty new to doing my own electrical and have done a fair amount of research but wanted to make sure im doing it right and have a question. I recently did a 99+ center console swap on my 96 4runner. And the center console i got had rear heat but my 4runner doesn't have it, so I want to get rid of the rear controls and add 2 USB ports, and 3 -12v sockets in their place. I figured the easiest way to wire it all would be to get a 6 way blue sea fuse block and mount it inside center console where heater blower would have been. So that way I'm only sending one big 10g or 8g power wire through the fire wall. I will install 100A circuit breaker near the battery for protection, and ground all the wires to the center console lower metal mount. I got a lot of my questions answered reading other threads, but all those people were setting up fuse blocks for lights winches and other high power draw items and had a bunch of relays. My question is do I need relays in my system somewhere or is what I stated above all I need to do?

I'm far from an EE, but I've done my fair share of wiring (motorcycle mechanic for a few decades, those guys love their "farkles").

The Very over-simplified answer is that you only need a relay when the draw is greater than the wiring (or switch) can handle. Most of the time this is used to fight voltage drop... I'll use lights as an example. Every 1vdc drop is like losing 33% of the light output. If you ran the power from the battery inside to the switch and back to the lights, you'd need more expensive (and heavier) wire, run a switch that can handle a higher load (and will still fail earlier) AND have dimmer lights. But by using a relay, you can have the shortest run from battery to lights as possible and just trigger that relay with light wire and light duty switches.

In your application, if you're going to run those outlets as all Switched, it would make sense to have a big relay at the battery that's powered/triggered to only come on when the vehicle is running. The way you're designing it though, there's no reason for relays inside. You'll have short runs of wire, can use higher gauge (thicker) wire without issue and not have a problem. Even if you want to switch those outlets, 12v 20a spst or spdt switches are cheap and readily available (you'll be hard pressed to find something that will pull more than 10amps on a 12v circuit, I've never seen anything that would). Be careful about sizing your main fuse, feels like 100a is way too much for 40amps (max) of load.

Just a FWIW because I've been there and done that, 12v sockets suck. They are just an awful design where you have zero "positive connection", they simply wiggle loose while driving. If you're thinking on relying on one for something like a fridge, you're in for a bad day when you find it's been unplugged all day. Ditto if you're charging some battery source for use when parked... Having one 12v socket for the random whatever is fine, but you really ought to consider a better connector and just modify anything you own to fit that new connector. Consider an SAE 2-pin connector instead:

Amazon.com: Electop SAE Power Socket Sidewall Port, Weatherproof SAE Quick Connect Solar Panel Mount Universal Flush-Mountable Connector, 12AWG SAE Cable with 8 Screws for Solar Generator Battery Charger (2 Pack): Automotive

There are other options too, but none that are "pretty" like those flushmounts. If you want a locking connector and happen to be handy with a 3d printer, you'd be golden. 2-pin SAE connectors stay together well enough for off-road motorcycle use though (I run my heated vest off one), so they would be fine IN the 4R too.

Hot damn, I need to get one of those for my Camry (small battery, not driven often, always on the Battery Tender). Put it in a hidden spot under the bumper cover - easy plug it without opening the hood or having a cord hanging out!

As for the original poster - You'll probably want 1 relay that is triggered by ACC or IGN power (you choose). You might also consider having one or more of the connections constant powered so you can charge something while the truck is off. So, that would be one big wire from the battery, fused near the battery for main power and one small wire from accessory or ignition power to trigger a relay mounted with/on a power distribution fuse block to your charger ports.

The blower for the rear heat is located under the passenger seat, not in the console. You can probably pretty easily mount something accessible there under the passenger seat for fuses/etc. where those of us with rear heat have no room.

-Charlie

I don't love under the seat for wiring and gadgets etc., easily wetted or damaged. To each their own though.

Take a look at where I put a panel under the glove box. It was totally wasted space in there and things are not going to get damaged at all. Best of all is that it is not visible unless you are on your back in the passenger footwell. I like to keep things looking as stock as possible.

Interior Aux. Fuse Panel Install

Thank you for info. I am planning on running them with no switches, straight to fuse block which im planning to have under/inside center console. And then one 10awg or 8awg (not sure yet) going through firewall to the circuit breaker, and then to the battery. I would like these sockets to always have power. I only chose a 100a breaker because the fuse block is rated for 100a, but your right I should base my breaker on what I'm planning on using. So would a 50 amp circuit breaker be what I want? Or even smaller than that?
I may hook other things to the fuse block later but for now its just the 12v sockets and USB plugs. I plan to use them for charging, powering interior led lights, and so I can plug my baofeng radio in (i have a battery pack that gets constant power by pluging into 12v). Plus USB for back seat passengers to charge their phones.

You need a few bits of info. total wire length installed and total load at maximum use/draw. With the total load you'll know the minimum wire size. 8ga for 30amps at 12 feet, most 12v sockets are 10amp and a double usb is usually 3 or 4 amps ~ so you're over 30a, might need 6ga which bumps up to 50a for the same 12 feet (or larger if you think you might expand later). ALWAYS size your breaker/fuse so it goes before the wire. Not good to have a wire that's melting away and catching fire just because you sized the breaker too big.

Be aware that the alternator only has so much to give. I have never paid attention, but it wouldn't surprise me if it's only ~50amps extra. That needs to be considered while doing this as well. If you really want to play roulette, you can juggle loads (I do this in my camper van, charge the house batteries while disabling other outlets in the van, all done via relay).

From rough estimates, looks like I'll need around 8 feet of wire from battery to fuse block. Wires from fuse block to sockets will be only a few inches. So from the wire calculators I've looked at 8awg should be enough to handle what I wana do. Since like you said each 12v will be 10 amps and the double usb will be 5 amp max. So if my max amp is 35 amps, do I get a 35 amp circuit breaker, or a 30 amp circuit breaker so it breaks before my max amp load?