I did start a Big Three install for my some day upgrade Alternator, but just have the two Ground wires done at this point because I have not pulled the trigger on the Mechman 250 Amp High Output Alternator For GM Truck 05-13 yet. Having an Odyssey ODP-AGM75-86 with the extra side terminals makes the Big Three addition a simple task.

I was getting strange output from the OEM before I started the project figuring the original Alternator was going down, or thinking about it. I cleaned everything up and..... back to normal for now so nor hurry on that Mod.

I am going to do a Big Three Alpha H3 thread when I complete it. I can tell you that you will need 7 feet of your choice Battery Ground Wire, 3/8" and 5/16" Ring Terminals, and the ability to cut, clamp/solder them. I am sitting on 2 feet of positive 1 Ga. Battery Wire and a 250 Amp ANL Fuse with ANL Fuse Holder to be used when the Alternator meets the truck. That will do it with a minimal amount left over.

Of that 7 feet of ground wire you will be left with about 3.5". You need to make or buy the lengths. I wrote the info in my iPad notes so I will update from there when I get to it.

That is: Alternator to Battery 45” with 3/8” Ring Terminals each end; and,
Frame ground 35.5” 3/8” Ring Terminal at one end, 5/16” at the other.

I used 4Ga Ground wire with BLACK BRAIDED EXPANDABLE FLEX SLEEVE WIRING HARNESS LOOM (which is the stuff to use in place of old school plastic loom) and it still allows the added Grounds to pass through the RVC. Note the BOLD, that chit is IMPORTANT! By pass that and you will have trouble as the H3s charging system is PCM controlled and the RVC is what monitors output. Do whatever you want, but I spent the time reading the tech articles and bulletins to do it correctly.


Battery ground to Alternator Mount Bolt after passing through the RVC.


Battery ground to Frame after passing through the RVC -- right next to the top front shock mount.