So I was on a mission to find a good ground in the trunk/back seat area as others have done and have an unfortunate finding: factory grounds suck. I used my Fluke multimeter and was getting 3.2 ohms resistance between the battery and the bolts behind the tire kit and back seat. This was after zeroing out the resistance of my test wire. I thought this was pretty awful so I went to discover where it was being introduced. I then checked the factory ground under the hood and found that the two I tested (pass side unibody and pass side near strut tower bar) had resistances of 2.7 ohms. Could the factory ground be this bad? If so, I def have to replace them. I read the diy grounding kit and think that's probably the way to go. Has anyone else tested their grounds and found them to be so terrible?

Held up on a project...

 

Yeah they vary from car to car, i was getting about 1 ohm everywhere in the trunk, decided to just run a wire back to the battery. - haven't regretted it yet...

 

did you run it with your power? I have my 4awg through the grommet in the firewall on the drivers side and i'd like the ground down the other side but don't really want to drill...

what gauge did you run and did you try it both ways? with 1ohm resistance and with a direct connection? did you upgrade factory ground at all? I just found about 20ft of 4awg oxygen-free stranded cable in my house and thought i should just replace all the factory stuff while i'm playing around with grounds anyway...

 

Yeah I thought about replacing all the (major) grounds, but i'm not lol.

I ran both my power and ground as 4awg and both down the driverside through the grommet - i did have to cut the plastic clips under the door thing to get them both to fit under there, but they do. - the passenger side would be much easier though, even though there IS drilling, there isn't any wires or anything in the thing under the door, so you can easaly fit all the wires in there..

 

Check my post in the ground sticky. If your battery was connected, the draw on the battery from the trunk light is messing w/ you.

 

i forgot about that. i read your sticky a few times last month before i was ready to start messing with things...

do i have to disconnect the battery to get a proper reading or can i do it some other way?

i redid all the grounds in the engine bay this evening with some nice 4awg cable. it's too late and dark to test the resistance right now, but i'll have a go tomorrow and report back.

thanks for the reminder though, i'll reread the thread and try again.

 

Been there, done that:

https://www.rx8club.com/showpost.php...9&postcount=58

 

Try removing the trunk bulb, making sure all doors are closed, lights are off etc., and try again.

 

Thanks man. That made a huge difference. Now i have 0-.1 ohms throughout the engine bay due to the upgraded grounds. I also have .1-.2ohms in the trunk without a dedicated line. That's good enough for me!

Now I just need to get the LOC hooked up and decide if it's better pre or post amp, otherwise I can try out my speaker level inputs. I didn't notice before, but my sub amp accepts front and rear speaker level inputs and low level rcas. Anyone know why?

I'd have it hooked up now, but I got rained on, so I'll have to wait awhile.

 

Cool. Glad it worked out. PRE AMP!!!!

 

yeah so i did try a few things last night after it dried out.

i used the navone ne-7v 2 channel loc.

first i tapped into the preamp fronts and found it to be clean and balanced, but too quiet

then i tried postamp rears and got a much better volume (still not great even at max gain) but the hu controls made it do weird things. at balance 0 is was quiet, but if you went more left or more right it got louder. weird. i tried to play with the trim pots, but one of them broke/was broken so can't test anymore.

then i tried postamp rears into speaker level input and found the same weirdness from the bose eq, but waaaay better sound and volume.


i'm at a loss now. i'll hook it up again with the speaker level inputs and try multiple locations (front/rear, pre/post amp) and see how it goes. i'll also return my navone for another one, probably the ne-774v 4 channel loc since my sub amp has front and rear inputs for some reason. dont know why.

i'm testing with the jbl 600.1 and a kicker solobaric s10l5 running at 2 ohms

thanks.

 

You don't need a LOC for the pre amp signals. You need a line driver for the best results.

A LOC takes high level signals and turns them to low level. Opposite of what you need for clean pre amp signals.

 

but i needed rca inputs to my amp, or so i thought at the time until i dug out another amp that had speaker level inputs.

i looked into line driver as thats what wikkedone suggested, but they're mad expensive too. might as well get something fancy like the lc7 or 6xs. i'm at the diy stage right now. use what i have lying around with a bit of elbow grease to get reasonable sound, not outstanding sound (yet).

anyway, i used the factory wiring diagrams you posted for someone else and was able to sort everything out from there. those were most helpful by the way! now i'm running speaker cable from the postamp rears to the rear speaker level input of my amp. (i still don't know why it has fronts as well, and i didn't know where the postamp fronts were on the factory wiring harness) this provides me with more than enough signal voltage for the amp and i can keep the gain way down. now i'm going to fiddle to get it sounding better and see if the bose eq drives me nuts or not. by the time i get over the thrill of the lows (even if they're nonideal) i'll be able to do this correctly with a line driver. yay!

thanks all for your help, cause now i got the beats.

 

I love it when a plan comes together.