if your front battery has good voltage at it i wouldn't point fingers at the alt, however if the power wires have had excess current pulled through them it may have slightly damaged the wires and raising the internal resistance in the cables, or a poor ground could be at fault. i would start be doing some resistance readings across the power cables and ground to frame cables as there is a problem with your voltage for sure.

now for the speakers cutting out if i remember the JL amps have good protection systems in them. one thing i believe they will protect against is low voltage so if the voltage drops below its threshold it will go into protection saving its internals from going up in smoke and would be why your highs are cutting out but wouldn't explain why your sub is not cutting out. another possible problem would be one that i have dealt with personally, i had a speaker in my tahoe that had a bad/loose connection internally and would randomly short and kill all my interior speakers power from the headunit, i would have to shut the radio off and turn it back on before the speakers would come back on and weather temps affected this as well seemed to do it more when it was cold out. i finally tracked it down to the rear passenger side speaker disconnected it and no problems with it for the past two weeks, now its time to replace both the rear 4x10 speakers with some 6.5's. hope this info helps you.

after everything cuts out if you go check your amp does it seem excessively hot? is there a protection light on?

 

No protection light and the amps aren't hot at all.

I will try checking the resistance readings. The grounds look fine but thats my only other idea of what could be wrong.

 

Hmm... if only your components amp is cuttin out and not your sub amp, the problem should be with the components amp. Have you checked all your wiring? Have you tried lowering the input sensativity/gain on your components amp? Are all audio enhancers such as loudness, SLA (sound level adjustment) off/0?

 

Wiring looks good as far as I can tell. And I have tried lowering sensitivity and it hasn't helped at all. When watching the volts with the DMM the problem clearly occurs when the volts just get too low (~9.6) then they jump back up the mid 10s usually and cut out briefly for like a second or two during this. I suspect this has what has been happening all along, but today they won't even raise back up past the mid 10s at the amp so they end up cutting out very constantly as the volts get too low. I don't know what would be causing this large discrepancy in voltage between the battery and amps. As far as I can tell the grounds seem fine (though I'm no expert, I just screwed my grounds for the amps onto two metal screws attached to my trunk roof. There is no evident paint or anything and it worked fine in the past before this problem started occurring.

 

it is a power transmission issue, too much of a voltage drop from the battery to be anything else, the JL is just more sensitive to it. clean and re-terminate the power wire and the ground points, frankly your ground termination doesn't sound good (as you describe it), try a point inside the body of the car as the trunk isnt designed to make good electrical contact with the car.

 

I have something else interesting to report

I tested my voltages with the car and amps off. ~12.8 at the battery AND at the amps. However upon turning the car in Acc. (and thus turning amps on) I read 12.4 on the car and 9.1 on the amps and with the car on (with no music playing) the battery voltage ranged from about 14.5 - 15.3. Yet the amp voltage ranged from about 11-11.5. What is going on here? Surely this must mean something but I don't know what. Why does voltage match when the amps are powered off but I lose so much once they get powered on? Is this a sign of bad grounds or what? I really don't know enough to tell.

 

Seems like your alternator isn't charging. Even though it's been about 11 months old, it will not last long if it has been abused. High current causes low voltage if the alternator isn't strong enough which will strain the alternator and lower it' life span. You do have a big voltage drop at the amps oppose to the readings you are getting from your battery. What type of power wire are you using? A bad ground and small power wire can cause voltage drop. Like I said before try reloacting your grounds to bare metal. If you remove the alternator, you can take it to an auto parts store and they usually check them for free or some auto parts can even check your alternator with this machince while the alternator is on your car. Normally alternators have a 1 year warranty if not life time warranty, if you diagnose the problem soon, you might be able to warranty your alternator.

 

If you haven't done the big 3 upgrade, I'd do that also using some OFC 1/0 power wire. It's a cheap upgrade to your electrical setup.
The Big 3 Upgrade – Improve your Car Audio Output up to 25% | Sonic Electronix Blog

 

Have had a really busy week and actually never got around to fooling with my amps, but I'm gonna try disconnecting the speaker amp tomm to see if my sub amp doesn't read normal when its powered alone.

But want to bump this just to see if anyone else has any ideas to throw out there. If I can't get this figured out soon, I might just take it into a car audio shop.

 

Do you have a distribution block? Have you seen if there's a drop before the amps? Have you inspected your power wire from the battery to the amps? How is everything wired? I apologize if you already covered this.

 

Glass fuse? Measure before and after the fuse under the hood... Maybe a faulty fuse..

 

I would also check the voltage before and after the dist block. if both amps are seeing the same voltage issue, chances are, the problem is with something they have in common. The JL amp with r.i.p.s technology will go into protection mode under 11v and shut off. I dont know anything about your sub amp, it may not have the same technology. with you mentioning the grounds are screwed into the trunk lid, I would redo the grounds to the bottom of the trunk (trunk floor)