Without drilling, where is the best place to ground an audio system?

I'm using a pre-existing hole near the seatbelt mechanism for the rear-left passenger, and used a bolt/nut to attach it.

I'm asking because my amplifier shuts off immediately after turning on (<1 second). I'm thinking I forgot to sand off the area before attaching the bolt.

Thanks!

 

i chose a flat spot underneath where my spare used to be, drilled a spot for the bolt to ground it with and sanded it down really well

 

I used the center bold for the child seat tethers. That trim panel should just pop up. No problems with ground at all, going on 5 years since I installed it.

 

I used under the child seat tether as well, sanded it down to bare metal and put it through the bolt there and that was that.

 

where the nuts screw onto the shock tower in the rear. (where the rear strut bars mount to)

 

Rear seatbelt eye bolt.