Voltage drop after big3

[Zak.vr6]

Basically I've used new 4awg from alt to bat/ bat to body/ and alt bracket to body

Before doing this I was getting 13.8v at the obd plug

Now I'm getting 13.2-3

Both at idle and whilst driving it really don't go up much

I cleaned all the Earth points

I just don't understand it as my bass is miles better at higher volume

Car has a 120amp alt

I'm running a 900w rms kenwood mono block amp

Yes I know there is a possibility that taking a voltage reading from the obd 2 port is not be best way to check

I do have 4/0awg power cables but the 4awg was a nightmare getting it in there without bulging

Thank you

[Zak.vr6]

by miles better I mean I've turned up the gain without any distortion

[Rich Schenk]

Why didn't you do alt bracket to battery negative, then battery negative to frame or shock tower. You should also do engine ground to battery negative. Body is usually thin metal and not a good ground

[Zak.vr6]

I need to wait till I'm back at work to crimp and solder more cable

What I've done today is move the Earth from the alt bracket

So now it's from the head to the neg to battery

And now it's reading 13v!! Lost 0.2v lol

I've not been playing the bass loud as running in a new sub

I'd just like to understand what's going on there

As lost 0.8v bit at a guess gained amperage as no distortion/clipping on higher volume