hu powering off and resetting

Hi there.  I've had this problem for a while, but never really bothered to fix it.  Because, at first I thought it was because of my subs, but that is not the problem.  Ok, so what happens is this:

1) I turn up the volume to about  21 on an alpine deck

2) deck begins to dim

3) I turn up to about 24

4) Deck/whole system turns off and reboots

So what I did, is I turned off my sub output so my subs were off, and turned the volume up.... it cut out and reboot again.  Then, I tried turning off the internal amp on the deck to my 4 regular speakers, leaving just my subs on, and I could crank it up.  No cut out.  So it is something between my deck and speakers, or my car and my deck.  Any ideas on what it would be though?  I just replaced the alternator and battery yesterday.  THANKS!

It's not one of those models that require the beefier power/ground wiring. Just a regular 18Wrms x 4.

What impedance are the door speakers? If they are 2ohm, this is the problem.

Either way, i'd run a dedicated power wire (fused at power source, of course) for the stereo. Ground it as best you can to sheetmetal behind the unit. This will solve your problem, unless your door speakers are less than 4ohm.