Amp grounding help

[Jezzey 10+ year member]

I'm installing a 600W RMS amplifier in my trunk and can't decide on a good place to ground. I have some pictures below. You will give to excuse the lack of lighting. I have limited daylight to work with this season so I lit up the area with my flashlight.

There are three holes in this piece of sheet metal located behind the side trunk liner. I could sand away the paint and put a bolt washer nut through it. The only problem is I'm not sure if the two piece of sheet metal have metal on metal contact. If they don't it isn't much of a ground.

This is also behind the side trunk liner about 6 inches from the back of the rear seats. I'm not sure how good of a ground it is and what it is connected to (unless I take off the nut and the bolt is holding in something heavy and it drops...unlikely but I'm pretty terrible with mechanics).

I'm thinking this might be the best option. I have no idea what these yellow plugs are for (maybe if someone has a clue let me know), but if you pull one out, there is a nice hole that I could find a bolt for. It looks like I have about three inches of depth before another layer of the body of the car (so I should be able to avoid rust). I would probably find a nice size bolt, a washer, and a lock washer. Sand the paint away. Put the terminal against it. Would a small spot weld to make sure it doesn't loosen (but not so much that I can't pry it off) be overkill?

There are two bolts. One is for the base of the seat (nice bare metal, but I can't imagine it being a sufficient ground). The other one I believe is for the seat belt bracket. No idea if there are consequences for loosening this bolt.

These bolts are next to the tire well. The closer bolt would be nice metal on metal if sanded. I have no idea what it goes to and if it is ok to remove temporarily. The rear bolt is so-so looking.

Let me know what you think.

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[SyKo13 5,000+ posts]

One with the least resistance

 

[audiobaun 5,000+ posts]

Can you take a pic of the Spare tire well area/remove the spare tire?id like to see the attatched bolt down for the spare tire base.i have used thids location on several trunk/hatchbacks,and can give you a detailed answer, if I can see it..It will be very simple for you to do,and works very well

 

[keep_hope_alive Premium Member]

i prefer the floor over the side (sides are tack-welded on in few places, thin metal, and usually offer higher resistance to the battery).

to use a bolt on the floor you'll need access to both sides. if you do that, put the bolt head under the car and have the threads on the inside (so the threads don't rust). you can coat the outside portion (bolt head and washer) with silicone to prevent water/rust.

i never use seatbelt bolts. those are safety restraints and adding ring terminals, sanding, etc. weakens integrity.

 

[maylar 10+ year member]

Also consider drilling your own hole and using a big self tapping bolt. Works for me.