My rig is an '86, and I'm going to add a couple extra 12v outlets in the front and rear. I'm aware that I can buy splitters and extension cords, but I'd rather do it right. I'm handy, but I don't know electronics worth a darn, so any input is welcome.

I'm planning on bringing a 10ga wire straight off my battery with an inline fuse, to a fuse box in the glovebox or down by the ecm, where I'll tap a single pair for each socket I'm adding. I know I could probably find an always-on power source in the cab to tap into, but I'd be worried about overloading it. I'm also anticipating transferring the fuse box to an auxiliary battery, but that's in the future.

1) How do I get through the firewall? Every entrance to the cab I can find is sealed up nice and tight, which I like. I'd like for the entrance I'm going to add to be sealed up nice and tight too.

2) 10ga supply wire... overkill? Not enough?

3) Inline fuse... 30 amp?

4) Anything I've overlooked?

I haven't added up the power demand, but I could conceivably be powering a GPS, MP3 player, and laptop, while charging 2 cell phones.

Nobody? I'm going to blame you all when I electrocute myself.

I suppose I will throw in a comment on this one.

I am not familiar with the 86' runner but it probably has an auxiliary grommet on the firewall. Mine 98' has it almost half way in the center, maybe a bit closer to drivers side. I would cut a small hole in the center and run your power wires through it, I like to seal mine with a bit of silicone when done. Be aware this stuff stinks for the first couple of days while drying but will make a great seal.

10 Ga wire should do fine, you will loose a bit of voltage the longer your run but I power a Ham Radio off the same stuff and it probably hogs more than you will use.

Check the power requirements for the things you will be using, you don't want a fuse that is too big so as to allow it to cook your stuff if you get a short or something. I know a laptop runs about 30-60ish watts the others couldn't be much.

I would think 15 amp would be closer to what you would want but may be off. Also, be sure to use a fast blow fuse, that prevents damage IMO. Also I like to add a fuse to the negative as well, it doesn't cost much and sure doesn't hurt. My ham Radios always have a fuse right at the radio as well as the 2 right by the Battery, again, cheap insurance against a short.

Maxil

What does the fuse on the ground do?

-The ground fuse just provides an extra layer of protection.
-IMHO Maxil is technically correct about using one but I probably wouldn't bother. Most don't unless they are wiring expensive electronics like Ham radios.
-I might opt for a 20amp fuse but I doubt I'd go much higher. You mentioned placing the fuse inside. I would highly recommend putting the fuse close to the battery. The closer the better IMHO. Why? Anytime aftermarket wires are run there's a risk of abrasion and a short. The farther away from the battery the fuse is the more "unprotected" wire you have which increases potential for fire. An additional fuse downstream never hurts. I would chose a rating inline with your 12v outlets. If they say 15amp on them then 15amp fuse. If you don't want to fuse each outlet than maybe a 25 underhood and a 20 where you split off the wires to each outlet. With 10ga wire 30amp under the hood is the highest I'd consider and 20amp inside to be safe. Truth is, one 20amp underhood is probably how I'd do the job. If my total draw required me to use a 30amp underhood I would fuse each outlet at 15amp. On one hand you don't want to over-engineer it, make it excessively complex etc. On the other hand you don't want to burn you truck either...
-You said you were handy but not electrical. I offer the following: 1) Poor connections = heat. Heat is the enemy. Wherever possible use one piece of wire, solder, make tight connections etc. 2) If I use a non-heatshrink connector I like to dab some silicone sealant in the ends. If I use a house style wire nut I silicone those too. It keeps salt, salt air and moisture out. The adhesive aspect also helps to keep the connector connected. Maybe that's overkill but boat trailers have taught me that it really does work well.

I think I said inline, not inside. And yeah, I've currently got a 15 amp fuse about 13 inches from the battery, screwed to the fender. From there I've gone through the fender (added a grommet) and down along the chassis to the passenger footboard, where there is an existing access hole.

I've added a fuse block under the dash, and fused 3 sockets at 7.5 amp each, and everything appears to be groovy.

Thanks for the tip on the silicone, I may go back and do that.

That sounds great! I misread your OP. I initially thought you were going to put the 1st inline fuse near the glovebox

I would agree, it isn't neccesary at all but makes me feel better. I can't afford to replace my Ham radio and if it gives me a 1 in 100 chance of saving it in a short, it's worth the $2 I paid for it, most people wouldn't bother with it though.

The other nice thing about fusing right at the battery, is if you do blow a fuse, it is easy to get to.

Again, good tips on the silicone Cj3Flyr

Maxil