Dear Everybody: Help me with my 4 channel!

I always add an additional ground to the headunit even if its grounded through the harness. I will usually "T" in a ground to the harness and ground it out to the chassis behind the headunit.

Grounds are typically the problem and solution to many automotive electrical issues.

 

Might be clipping and throwing your amp into protect...

I'm not a big fan of settin gains by the math. I've tried it probably a dozen times and it never seems to go as right as doin it by ear.

At what point do your speakers cut out? 75% of max volume? 80%? 95%? depending on how high you hvae it turned up, your head unit could be clipping the signal from whatever medium you're using and passing it through your amplifier. If you have a newerish amplifier, they generally recognize a clipped signal and shut it down rather than amplifing a clipped signal.

If it's not clipping there, could be clipping at the amplifier if your gains are set too high.

I'd grab a few 0DB test tones for your speakers, whichever you prefer to use ( Personally, I use 45hz, 800hz, and 5k hz for mine ).

-Turn your gains all the way down.
-Put in a tone, 800hz or 5khz is probably easiest for this. Then start turning your head unit up until you hear it start to distort the signal. That's where your going to start clipping signals. So turn it back down a few notches (this should later be your max volume)
-Restart your tones. Use tones that only get sent to one speaker at a time ( I.E. subwoofer / mids / highs ). Just put it on repeat.
-Put your head unit at the same volume you got earlier for max before distortion, then start turning your gains up. When you hear the speaker start to distort, back the gain off alittle bit and move on to the next speaker.

Even if this doesn't fix your problem, it at least eliminates clipping at either the H/U or the Amplifier as a potential problem.

Let us know. If it's not that, may be a loose fuse somewhere, or something much simpler.