I was working on my A/C system recently and I noticed this loose wire in my engine compartment.  It ends in a metal loop and it's positioned near a screw hole in the engine compartment wall.  (There are two views of the same spot in the image below - one with annotations and one without.)

 

 

I can't imagine that normal driving would make a screw work itself all the way out.  But I did have the clutch replaced a year ago and maybe the mechanic forgot to reconnect that wire when he put everything back together.  But that would mean that I've been driving with the wire disconnected for the past year (without any noticeable problems).

 

Questions: Is this a ground wire?  Should I get a screw and (re-)connect the wire to that hole in the engine compartment wall?

 

Part of me says that if it ain't broke, don't fix it.  But part of me says that the ground wire probably serves a safety function and I'm risking an electrical short or a fire if I leave it disconnected.  What do you think?

Yes its a ground. No it's not a safety risk. The engine still has the main ground wire from the starter bracket to the battery, which should more than cover all of its grounding needs. That small one is likely for any interference or static buildup that may occur on the intake manifold.

 

Look on the top of the strut tower on that side and you should find a few more ground wires. If that one will reach there, that's probably where it should be bolted down.

 

 

The hole in the firewall near that wire is painted, so its unlikely there was anything bolted to that spot in the past.