I have an 800W Kenwood amp that runs two 4 ohm 12" Eclipse subs on a 2hm load.

My sub box is in my trunk, and my battery is right under the back seat, so the power and ground wire only goes about 4-5 feet if that. What size (gauge) wire would be best for this set up.

I was using 8 guage but i have a bunch of 4 gauge wire too. And do the power and ground need to be the same size or can I use 4 gauge for the power and 8 gauge for the ground? But if i have enough for 4 gauge for both I might as well just use all 4 gauge right?

yes 4 ga will be perfectly fine. epsecially if u already have it.

if you plan to upgrade eventually, you may consider 0, but with only 800 watts, ur fine with 4

4 for just the power or for both? is there any disadvantage to running 8 gauge as the ground and 4 as the power?

always run the ground the same as the pos. ALWAYS!.

it will work with 8, but not worth taking short cuts there, besides in dc, the electron go out the neg, and in the pos

your system will only be as strong as the weakest part, so even if you had 8 gauge on the power and 4 gauge on ground, it would kinda rule out the 4 gauge ground. go with 4 gauge on both power and ground and you will be fine.

That'* kind of what i figured...I got the gauge installed and my volt gauge doesn't move around nearly as much now, so I know i got a good connection. Thanks for the help.