4awg

I know there are some threads on this already but I’m looking for a specific answer regarding my setup, I’m doing a big 3 upgrade with 4 awg wire, should I fuse the battery to alternator wire, and what size/type considering 4 awg, also I’m not replacing factory wiring just adding to it, any help...

i been in the market for a new sub amp. i have two 12' jl w3v3 4 ohms i was running them at 2 ohms. with Kenwood Kac-9104d 1800max it sounded OK. i bought a MEMPHIS BELLE 16-MCD1000 and ended up selling my Kac-9104d before getting the memphis. i installed the belle but the amp wouldn't leave...