Grounding Not Included?

[Ewr101]

So I've just acquired a 72 2WD Blazer that's in really good condition. I don't have any MAJOR issues with it at all. I figured the first thing I want to redo is the 40+ year old wiring and fuse panel. I'm going to go with one of the more popular ones mentioned in this forum. My question is, after reading the instructions for a few of them they say that there are grounds that I'll need to install that are not provided with the harness. Can someone tell me how many there are, what they are, what gauge wire would be best to use? I'm just guessing but headlights and tail lights? I just want to know the full scope of work before I jump in with both feet. Thanks for your time.