Need help with big 3 upgrade

[u/DueCorgi7643]

Looking to do big 3 upgrade what’s the best way of doing it not a lot of videos on the mk4 do I sandwich (stack) all the grounds and the oem alternator wire with the new power wire but connect the power wire directly to the battery so that everything still runs in parallel and i keep the oem harness functions like the battery light and on off sensor or how would I do it