What's this ground wire(s) for?

This:

 

Injectors

 

Good to know. I've changed my plugs, wires and coils recently and it ran like poo. I started to have issues with putting the truck in reverse from drive and the truck completely shuts off like it was starving for something. I couldn't pin point the issues. The first time it happened I thought oh maybe because I used cheap eBay coil packs. I put back the stock Toyota ones and it still ran just fine a bit rough idle but it ran and didn't do the reverse to park to idle and it dies thing. Today (about a month) later since I went back to my stock Toyota coil packs it came back. I went through it all...took all the plugs out and checked them all. Did the passenger side first then proceeded to the driver side and noticed this screw was back out a bit and on the verge of coming off. Didn't think of it as the issue I went ahead and checked all the driver side plugs and wires and tighten it all up. Fired up, tried to duplicate the issue again but didn't. Thought back to this screw and I unscrewed it and tried to turn the truck over, I heard the truck trying to crank but not turn the engine on. Put the screw back, drove around the block and couldn't duplicate the same issue again so I wanted to know if this is the issue the first and second time so I start my truck and let it idle. Backed out the screw and the truck starved and died. Hopefully this was the issue but I still didn't know what it went too but I appreciate the quick reply:
https://vimeo.com/164846061

 

that's one clean engine bay.

 

I try LOL:

 

How the hell is that even possible to be that clean...

 

Lots of Simple Green, elbow grease, scrapped knuckles and Stoner Trim shine.

 

I had one 3.4 engine it just would not run correct till I connected the ECM ground to the battery a few years now with no problems