Two mono amp install = low output

[Vinny415]

So I recently added a second mono amp same make and model to match what I already had. I have two subs. Each sub is wired to each amp. The amplifiers have bass boost knobs. When I turn both knobs up I lose output to my subs. Why is this happening. Each amp gain was set using a multimeter (can’t afford an SMD DD-1 right now). Each amp should be pushing at least 750w rms at 1-ohm. Which is what was certified on the dyno, but like I said before, when I turn both of the amplifiers bass knobs up, it hits less than when my subs were running off 400w each!

[AaronT]

Cuzz your electrical can't support the current demands

[Vinny415]

I drive a 2015 Camaro SS and the alternator is sufficient. I am running 0 ga power to distribution block, then 4 ga to each amp. 4 ga grounds to grounding block which is then grounded with 0 ga to a good ground. Checked with multimeter. I smoked one sub earlier this week because I set gains without bass knobs installed and turned them up too high. Reset the gains to proper voltage with knobs turned all the way up so I could eliminate the possibility of turning up too high. 

[Vinny415]

UPDATE ::: So after a little research, I remembered watching a video by Mark at CAF talking about phasing and polarity. So I pulled it up again and saw that a common fix was that manufacturers sometimes install the wrong polarity terminals. So positive and negative is flipped. So I tried flipping my speaker wires to one of my subs and BOOM!!! Now my subs are hittin like they’re supposed to! Now if I could figure out a way to build a ported box for both 12s to fit in my small ass trunk and still have space for stuff...