Main Power Cable

Main Power Cable

Ok so i put in battery terminals a bit ago and i cut my main positive wire cable too short so i did a ghetto setup and i twisted on some 4 guage onto it and ducked taped it together.... so i know this is really ghetto but it worked but now the duck tape is coming off.... So wat i wanna do is this....

I wanna replace the main positive power cable.
From wat i can tell it runs from the alternator to the fuse box near the passenger headlight, then from there it runs to the battery.

So any advice on going about this?
Most likely i'm gonna just replace the wire coming from the fuse box to the battery with some 4 guage