What are all the battery ground wires for? 3 wires on each negative terminal.

A couple of days ago I couldn't start. Not even a click. Discovered the battery grounds were loose and corroded. I took each out of the clamp, cleaned them and tightened --- except for one wire in the right hand battery. I started the truck but it immediately idled very rough so I turned the engine off and found the wire I had let drop. After connecting that ground wire, the truck ran fine. So does this truck have systems that have separate ground circuits? What are they?

 

All the systems on any veh are shared by a ground, electrons take the easiest return to the battery, and since there is a huge resistance caused by the missing ground, it takes the path of least resistance (thru other components until it gets to ground ) poor grounds can cause a horrible electrical nightmare, causing systems to run poorly, or not work at all

 

So, it looks like each battery is supposed to have 3 grounding wires. And, it looks like they have separate ground distribution circuits. I notice one of these (from the auxiliary battery) services the pcm and injection pump (S109). I suppose that may have been the one I left unconnected and caused the rough run.