My 5Door Blaze DTurbo Project

[4WayDiablo]

Going to get a wiring loom out of a bmw 3 series thay got battery in boot

you dont need to do that
just go get something like 0awg wire and run it from your origional +ve connection on the battery to the boot, you could get a battery terminal and just connect the two
similar to the one in this pic... the red wire being the new one which will route to the boot (or wherever the battery is going to be

then the negative you ground to the body then upgrade earth straps
as for the battery in the boot, ground that to the body too hence the need for upgraded earth straps