Trying to locate a decent ground location for my amplifiers and it looks as though a bolt that is beneath the trunk floor should work. If are you are standing facing the trunk, it is about 6" from the back seat and about 10" in from the side underneath the foam padding there. Curious what this bolt is for, since it had red loctite on it and goes outside somewhere, the bottom half of mine was rusted and lacking in threads. Does it go to anything or just hold that bracket down?

Here is the bolt itself.

And a wider shot showing where it's located.

Oddly enough, it's a 13mm bolt on that side but on the passengers side is a 15mm nut. Just curious what it is for and hoping I can use it as the ground location, using a multimeter on it to test my switched 12V it worked well, but again, I am curious what it is for.