Probably not if you went to a non switched line. The fusebox is fed directly from the battery, so depending on which circuits were included in the "protection" feature, you may end up bypassing it all together. You'd really have to read into the wiring diagrams etc to be sure on that count.

 

Actually it is not needed directly near the battery, but it best. Most vehicles have the fuses under the dash 2-5 feet away from the battery, which is not very close. Think of the head lights, marker light and TONS of other systems are closer to the battery than the fuse is. So your concept doesn't make sense.

The only reason it is best to be close to the battery is if there is a short you want it to blow the fuse, but if the short before the fuse it will burn up the wires which will burn up way before the battery cooks or blows. What ever is around the wire has a chance of catching on fire which can carry to the entire vehicle.

The true purpose of fuses is to protect/contain all wires/systems from frying from one short. Which could cause a fire, everywhere. The vehicle fire will cook and may blow the battery.

So your condom analogy doesn't play out in this. If anything a fuse far from the battery is like a condom with little lube, it works but if there is a problem it can burn things up.

 

I'll agree some vehicles have fuses under the dash, but there is ALWAYS a master fuse on the main feed line that is in close proximity to the battery. The fuses under the dash are secondary and stepdowns from the initial larger rated master fuse. The concept is 100% proven and sound.

As for fuses protecting the wires from burning up vs protecting the battery from burning up, that depends on the size of the wire. if your using 18g wire yeah, its probably gonna cook off in which case the fuse could save the wire, but if your running 10g or better, the battery also becomes a major concern.

I've been playin with wiring for over 20 years now, Trust me on this one... you want the fuse as close to the power source as possible.

 

Ok so enough of the this way that way with the fuse... I get it. What gauge wire is best. Thanks!

 

Considering the length of the run, I'd probably suggest 14 or 16 gauge wire. You could probably get away with 18 gauge, but 20 gauge would be pushin it.

14 Gauge
http://www.parts-express.com/pe/show...number=100-060

16 Gauge
http://www.parts-express.com/pe/show...number=100-055

 

The fuse is there to protect the wire; it should be close to the battery. If the fuse is located back in the bed area, there is a lot of wire between the battery and the fuse that can potentially short out and catch on fire. The shorter the distance between the battery and the fuse, the smaller the likelihood that a short will happen between the battery and fuse. Ideally one would use a fused battery terminal clamp which is the best possible protection, though installing the fuse within a foot or so of the battery is acceptable.

If you plan to be powering devices which have large power requirements, be sure to use a suitably large gauge of wire to minimize voltage drop, and overheating of the wire. Also, if you plan to be powering such devices without the vehicle's engine running, you will need a suitable battery. A normal starting (SLI) battery is not suitable; you will kill it in short order. You will need a deep cycle battery, or a battery with some deep cycle properties, such as an Optima Yellow Top; which is a good choice if you only have one battery, because it works well as an SLI battery too (which is the reason they are popular with the car audio crowd).

How can you recommend a wire size without knowing what sort of devices he plans to power? If he's plugging in a 1 kW device, he would want at least 4 AWG wire, for example.

 

That's what I was thinking. I've got a DIY on off-road lights out here somewhere that has the break-down on figuring out amp draw from wattage and then what gauge wire you should use for that anticipated amp draw.

Might be appropro here as well, just skip over the light wiring diagrams...

https://dodgeforum.com/forum/3rd-gen...nd-relays.html




And yes, whenever possible, you want to place an in-line fuse as close to the power source as you can. The reason is power degrades the further you run it along a wire, so an overdraw of current will be seen faster and closer to the power source, giving better protection. We are talking milliseconds here, and 99% of the time it's not much of a factor, but there is always that 1%...

 

He said it awhile ago. He wants it for light duty draws

 

Ah, I missed that. Assuming he is talking about something like an ordinary car radio (without an external amplifier), then yeah, 14 AWG would be fine, though I would probably use 12 AWG just to be on the safe side. On the other hand, if the radio is more powerful, like say, 100 watts, he would want at least 10 AWG.

Also, he is going to have to ground that outlet. Since it is going to the bed and presumably being run under the truck in order to get there, grounding to the frame would give the best ground (there are usually places to bolt a ring terminal to on a frame without having to drill). Use the same size wire for ground as is used for the power wire.

Here is another wire size reference chart from The12Volt.com - Recommended Cable Size by Power and Distance.

 

If you are so concerned about where to put the fuse, just put one on each end lol.