Thanks, going to be even better when I use 1 AWG on everything.
Will be 1 AWG with a 250 AMP fuse running to the isolator in back, then two 4 AWG positives coming from the second battery, both properly fused as they come from the isolator, running to the 2 AMPS I have...

Started on this today, I still have to run my alternator wire a bit better, I have some zip ties and wire loom coming...
I got the batt'* ground done.
The other chassis to batt ground is a 15mm bolt, and it is stuck, going to try to soak it with some PB...
If I cannot loosen it I'll find another nut the same size, and there are just enough threads to add the wire..
I went with 1/0 AWG, and nice heavy duty copper ends...

Keep an eye out for the fuse holder. Mine had a melt down eek!

re any loose copper wires, better off with proper, terminals ends.

I have two fuse holders and fuses, I was not sure if there was a need to fuse the run to the alt, as it is not fused to start with.
I have wire loom coming for the alt to batt run, and the other grounds..
Should I fuse the batt to alternator run?
I have not seen anywhere mentioning doing so with the big 3 upgrade yet..

But for my run to the trunk, it will be fused with a 250A fuse, since my ALT can deliver 250A...
Then from the isolator the AMP'* wires will fuse from it..

No need to fuse the run from Battery to Alt.
Any cabin or trunk runs etc keep an eye out for any fuse holder melt downs.

Yeah, that is why I always make sure my fuses can handle just what the AMP calls for, that way any more voltage than that and the fuses should blow, granted things don't always happen that way, but I'll do it as safe as I can...
I am replacing my top terminals soon, and putting on some side terminal connectors to help make my wiring cleaner, and get some of it away from the top of the batt area, as I am running out if room there, lol

Ampper Brass Battery Terminals Connectors Clamps, Top Post Battery Terminal Protector Set for Marine Car Boat RV Vehicles

https://www.amazon.com/gp/product/B07PPGBXG4/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

Vgate 6x1/0 AWG Gauge Post Battery Terminals for Lithium or AGM Lead Acid Battery with Bolt Down Ends or Threaded Studs M10 or 3/8”-16

https://www.amazon.com/gp/product/B08PTXCQSX/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1




These will be in the trunk on the DieHard Platinum AGM.

SUNMORN Battery Terminal Connector, 0/4/8/10 Gauge Heavy Duty AMP Car Battery Terminals Connectors, Shims Positive & Negative

250 AMP Intelligent Dual Battery Isolator Universal 12V 24V VSR Voltage Sensitive Relay for Car, Truck, ATV, Emergency Battery Starter Controller Heavy Duty Power Switch Charge Relay

https://www.amazon.com/gp/product/B08H21FCV7/ref=ppx_yo_dt_b_asin_title_o07_s01?ie=UTF8&psc=1




My fuses for the 1/0 AWG run to the trunk.

TopstrongGear Solid Brass 0/2/4 Gauge 250Amp ANL Fuse Holder with 250Amp Fuses(2 Pack) (250 Amp)

https://www.amazon.com/gp/product/B07XRLFWN7/ref=ppx_yo_dt_b_asin_title_o06_s01?ie=UTF8&psc=1



I am using these terminals, good thing I bought that crimper that can do up to 1/0 AWG wire.

SELTERM UL Listed Heavy Duty Wire Lugs, Battery Cable Ends, Bare Copper Eyelets, Tubular Ring Terminals, Closed End Crimp Connectors

https://www.amazon.com/gp/product/B073Y75H66/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1



And the wire...
I used this on that short run to the ALT, hopefully the 20' left is enough to get to my trunk, if not I buy another 25', I do not like the idea of patching cables together, I want straight runs, no breaks...

InstallGear 1/0 Gauge Blue 25ft Power/Ground Wire True Spec and Soft Touch Cable

https://www.amazon.com/gp/product/B07B8P14DW/ref=ppx_yo_dt_b_asin_title_o05_s01?ie=UTF8&psc=1

InstallGear 1/0 Gauge Black 25ft Power/Ground Wire True Spec and Soft Touch Cable

https://www.amazon.com/gp/product/B01CSYF06Y/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1



Oh yeah, the wire loom for the engine bay..

Alex Tech 10ft – 1 inch Split Wire Loom Tubing Wire Conduit – Black

https://www.amazon.com/gp/product/B07TDBF299/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Pretty sure 1" will cover the 1/0 AWG nicely...
I had 3/4" and it came close...