Just checked and I have red and black scosche
number 4 wire. Probably could go a little smaller but I guess the larger can't hurt.

 

You've got that right... can't have enough fuses... I'd rather fuse blow then my truck catching fire...

 

Ford does not specify what size it is.

 

I know its not bigger than a number 4 wire and theres alot more running off the main panel than I will be running off this sub panel. Might just get some #6 wire.

 

You guess it is not bigger than 4 AWG.
- Dangerous game to play with current draw.

Look at 14/3 SO cord and 12/3 SJOOW cord next to each other.

They look the same from the outside, even using calipers. Does not make them the same.

Your truck, you can do what you want to with it, 105* automotive 6 AWG is good for no more than 70A in short lengths. If you go with 6 AWG 90* THHN wire from Home Depot, it will be lower.

 

Ford figured out what allowing a high resistance short to ground does to a bank account with the 97-03 MYs.
- Over sizing a fuse is just as dangerous as not fusing a circuit.

 

Yeah, they learned the hard way.

I used to go on the low end of the rating. I'd rather have it blow. I've always go on the limb and go with a 15 amp fuse, and if it blows 3 consecutive times, and there is nothing wrong, then I'll ramp it up another 5 amps.

But since then I do the math and use my amp-meter, and from that I will know exactly what the current draw is.

 

The reason I say its not bigger than 4 wire is I don't see any wires bigger than that going thru the fire wall and it would have to come from under the hood.

 

Does your 2006 have AWG markings on the Yellow w/ light green wire ?
- My 2006 MY F150 does not.

 

Where is that wire your talking about located.

 

From the battery to the CJB through the firewall.

That is the main feed to the CJB.

It is still guessing that it is not larger than 4 AWG, using the drive by look at the wire.
- Can't visually confirm what AWG wire is.

 

My friends a master tech at ford so I'll ask him and see if he knows

 

i'll throw in my 2 cent - and i'm a licensed master electrician

first - wire construction - insulation thickness changes based on use
and wire gauge is based on ability to handle heat, that said - 4 ga wire has a higher amp rating then 12 ga.(i'm sure you knew this already)

second - types of wire - automotive wire is made up of more strands, this allows them to handle vibration better and insulation due to higher eng. compartment temps. commercial/house wiring uses thicker strands and is very stiff and insulation is commonly rated at only 90*c ( it's allot hotter
under the hood on a summer day)

manufactures use cost controls which means bare minimium. wires sized for the max load with time limits so it's ok if it heats up a little.

if you are adding curciuts, wire and protect them with propperly sized wire and fuses this will help in propper operation and IF something does happen to go wrong your insurance would be less likely to deny claim.

as a vol. firefighter (20+ yrs) i've seen plenty of eng. compartment fires started by wiring and always the same "i just had that installed" which means they did it them selves.

so yes- use larger then 4ga and fuse the battery leed at 100 amp and use automotive wire. crimp connections if possible or use a good mechanical connector, use corrosion protection on finished items.