Batteries..

[garretttt4 10+ year member]

Yes, to frame is one way of doing it. Not the only way and possibly not the best way.

Yeah I'm sure it wasn't the best way but it was the first time doing two batteries and I only had so much wire lol

 

[mlstrass 5,000+ posts]

This really doesn't make sense unless the wires were too small to carry the current trying to travel across those wires. I'm not saying you didn't see that fix an issue, but it's hard to believe something else wasn't wrong. If it's grounded to an actual frame, that could be better provided the connections to the frame are real good, but I would hesitate to say a unibody car would be better than proper dedicated runs of wire.

one set up was 2 runs of 1/0, 2nd set up was 4 runs 1/0 + 1 run of 4/0

Both had weird signal issues with the sub amps. After swapping EVERYTHING in the signal chain I tried grounding in back and problem went away both times. I only tried that after reading of a few others who have had problems with running grounds front to back...

I run 20kw+ with grounds in the back and it's a unibody vehicle (mini van), so no real frame. Works fine...