Installing a head unit in a jeep wrangler 1998.There are two wires that are

[Johnny towtone]

attached directly behind a screw? What are they for? All the rest a attached to to white and black wire harness. These two though a attached with a circular medal end to the wire that is placed behinds a screw attached to the stock head unit.

 

[The "D"]

its a ground wire. put it back under the screw.

 

[Kmax]

Ground wires.