how to wire dual alts and extra batteries

[BAMBAM]

noob here, first post, brand new mechman customer.

now what i have purchased is a dual alt bracket from DC Power, two 270 amp alternators from mechman, and a XS Power D3100. now i already have the bracket and both alternators installed. but what i am having problems with is how am i supposed to wire both alternators. i was told to use one alternator for the car, and the second alternator for the system. so i have the first alternator wired and powering the stock electrical, which includes the headunit. the second alternator was to power the system so the door speaker amp and the subwoofer amp. it is wired to the XS D3100 in the trunk but i cant get the second alternator to run. i was told the bracket should be sufficient ground for the alternator. i dont know if this is true or not.

and then someone told me i should have wired both alternators together.

problem is, ive read up and tried to do research but its blind leading the blind. im new to car audio, but ive always been a quick learner. someone please help me out? how should i be wiring both of these alternators?

the single D3100 is not the plan, it is just battery 1 for the setup i am trying to go for.

[TeamHT]

what amps are you runnins? how many subs? the mechman alternators do come with a positive and ground post. should have already some bolts on there. out of curiousity, big 3 done?

[BAMBAM]

I'm running three 18 aq hd3s with a sundown 4500. I do have the big 3 done thanks to the tutorial on this site!

But I'm still lost as to how I should wire my setup or what is needed. I will be adding another sundown 4500 which was why im trying to get the electrical set up first.