I relocated my battery to the trunk a couple months ago and i am yet still to properly wire my alternator. The way i have it setup now if i were to cutoff my switch my car would still run off the alternator which is not what i want, its not safe either. I need to run my big power wire from my alternator to the battery side of the switch my question is what size wire should i run and where to get it?

depends on the alternator rating and the electrical load
-if it's a stock alternator and close to stock electrical load
6 or 4 GA should do it,i'd lean towards the 4 GA if you
pull more than 70a often.Be sure to put a fuse of about
200a on the alt end.
my local farm/ranch store has wire suitable,other stores
to check include welding shops,RV shops,car stereo,4x4,
industrial electric shops etc.

i only have the basics like power windows power door locks, soon to be installed msd 6al-2 programmable box, electric fans, electric fuel pump, no subs or amps. do you think 6 gauge will do? i hate running thick wires under the carpet haha

6 ga should be good,sounds like you will be under 50a
most of the time

thanks for all your help, do you think i should run an inline fuse?

I would definitely have a fuse in-line when running wire that length. Cheap insurance when playing with lots of power

Also, there's more than enough room under the door sills for 4ga to be run. There are channels for the factory wiring under there that can be used just for a job like this. It never hurts to go too big.

i'm a wire noob, i beleive the power wire from the cut off switch to the engine bay is 2 ga, should i have a fuse on that?? and for the 4 ga wire for the starter can i use a car amp 4 ga wire? and a 200amp fuse 12" from the alternator?

any time you have a power wire wire carrying a sizable amount of amperage, you should fuse it. It doesn't take much to cut the insulation and short out to the body, especially when around moving parts and going through body panels (remember to always use grommits!). Its much cheaper to replace a fuse than a car. As for the size of the fuse, never exceed the amperage rating for the length and gauge. Dug this chart up to demostrate the MAX ratings of wire by length.

wow this is interesting, i do not have a way to measure my amperage draw, i think my multimeter will only go up to like 10 or so amps, i have a 2 gauge wire from cut off switch to under the hood about 16' long, and i will now be running a 4ga wire from the starter to the battery side of the cutoff switch. would i be ok getting a 200amp inline fuse for the 2 ga wire and a 100amp fuse for the alternator wire??

100a fuse will be good for the alternator wire,200a
might be marginal for the starter wiring unless you are
using one of those japanese gear reduction starters
-just try it, if 200a blows,up it to a 300a