Ground Wire? Quick Question

What is this ground wire for? And what effect would it have if left as is?

 

You talking about the one on the fender with the yellow ring terminal? It's aftermarket and could be for anything.

 

There should be a wire running to that bolt from the negative post terminal.

 

Ya, no telling what the loose strands are from.

But your truck needs to have solid ground wires running from the battery to the body as well as to the engine.
The heavy engine ground cable is not enough.

You also need to have a separate ground running from the body to the engine.

 

Sorry I should've been more descriptive. I'm talkin about the bunched up copper just above the yellow ring term.

It's been like this for as long as I can remember, I'm pretty sure at one point it was long enough to reach the negative wire but now it's just too short. I haven't noticed or seen any difference in my truck so i guess thats just why i've never really tried fixing it or finding out about it. Can someone post a pic of their negative wire and this ground? I just wanna be 100% sure. Thanks for all your guys feedback.

 

The bunched up copper strands appear to be left from cutting a second ground wire to the bolt attacking the black ground wire to the body of your truck. Since, the "bunch" is not connected to complete a circuit, it can be removed. Base on the size of the wire, the black ground wire appears to have been added to connect an aftermarket appliance such as an radio.