As I imagine you already know, with a multimeter you can check if it is a ground wire by 'continuity' between the eye terminal of the wire and the ground point that is on the C-pillar on the left side (preferably >
1 ), or the ground point that is in the compartment of the spare wheel, or any place on the body that you know is a good earth...
"biiiiip" >
example in 1:10.
Maybe I didn't understand your question correctly...
If it is a ground wire and everything works on the trunk lid you can insulate the wire with cloth tape (for aesthetic or noise reasons) or leave it as is (a ground point in that place is fine in case you need it for any retrofits).
By the way, I recommend that 683 multimeter that is sold on Aliexpress for between 22-25 euros, it is very easy and 'pleasant' to use, for beginners/novices or not, it is very precise, it has a rechargeable lithium battery that lasts infinitely, and it also has a great carrying bag/box.
It is NOT perfect for very demanding people, but it far exceeds any expectation for that cost.
![π](//cdn.jsdelivr.net/gh/twitter/twemoji@latest/assets/svg/1f385.svg)