Running a ground wire for a trunk subwoofer

[wrybread]

I'm getting materials together to install a subwoofer in the trunk of my s70 (not a body panel shaking sub, just something to add a bit of bass), and I'm wondering if people think I should run a ground wire from the battery, or if I can tap into the chassis ground somewhere? I vaguely remember reading that chassis ground isn't done anymore, but maybe that was wrong, or maybe 1998 predates "anymore".

Thoughts on finding a good ground spot in the trunk? And what you'd use to tap into it?

[misha]

Just ground it to a chasis somewhere in the trunk.
Scrub paint a bit to reveal bare metal and bolt it down.

[454cid]

Just ground it to a chasis somewhere in the trunk.
Scrub paint a bit to reveal bare metal and bolt it down.

I second this, and would add that it would be a great idea to clean/re-new the grounds in the engine compartment while you're at it.

[Goupil]

When I did the fuel pump wiring mod on mine, I used an existing grounding point under the rear seats. It's under the lower part of the seat, you need to lift some insulation padding to see it.

[Clemens]

My sub is grounded in the trunk area (or was it under the backseat?). I think the ground wire to the battery is for the nerdy audiophile group that almost got extinct 15 years ago.
Don't forget there is a really nice rubber grommet underneath the brake master cylinder where you can run your +12V wire through the firewall.

[MrAl]

I'm getting materials together to install a subwoofer in the trunk of my s70 (not a body panel shaking sub, just something to add a bit of bass), and I'm wondering if people think I should run a ground wire from the battery, or if I can tap into the chassis ground somewhere? I vaguely remember reading that chassis ground isn't done anymore, but maybe that was wrong, or maybe 1998 predates "anymore".

Thoughts on finding a good ground spot in the trunk? And what you'd use to tap into it?

Hi there,

Steel is not a great conductor not as good as wire grade copper which is fairly pure copper, but because the good conduction of current depends not only on the material but also on the cross sectional area that means if you increase the cross sectional area you can get a huge tub of butter to conduct well
Seriously the chassis will have a large cross sectional area so it should work well for a ground, which actually acts as one wire of the speaker that has to conduct current to the speaker. If there is some strange circumstance that does not work out well on your car you can always go back and replace it with a heavy gauge copper wire so nothing lost on trying.

If your speaker draws 120 watts peak then that would be 10 amps peak (engine not running), which is not really that high really. A 14 AWG wire would handle that well, or if you want to go to a 12 AWG wire that means even less drop. We can calculate the voltage drop and power loss for each gauge of wire if you like no problem.

[abscate]

M6 bolts holding down the fuel pump cover would make nice ground points

[BlackBart]

if you increase the cross sectional area you can get a huge tub of butter to conduct well

And THAT's why they call you Mr Amp!

[wrybread]

Cassis ground for the win! I even got fancy and used a terminal block in case I install another amp. For no good reason in hindsight, would have been easy enough to add more grounding points. Every time I browse the r/CarAV reddit I wind up buying some other gizmo I probably didn't need, ha.



Now if only I could figure out which of these wires in the rear lighting harness is the reverse lamp for my backup camera... That's been oddly hard to google.

[abscate]

It’s the one with 12 volts on it in reverse gear, with the ignition on…