Amp keeps turning itself down - cant turn off 'protection'

If it just started, you have an equipment or wiring problem. Check the wires first, that's easy. Otherwise, the amp may be bad, check the warranty if its new. Maybe you can get a replacement.

If it's always happened, some cars have an factory amp for the rear factory speakers hidden in the wiring. Sometimes between body panels. If you didn't bypass that, you're more than likely blowing out the new amp with too much power causing it to shut itself down. (protected mode or keep blowing fuses) Could be a blown speaker, bad ground, internal damage, RCA cable problem, the list goes on and on. Find out the preoutput voltage of your headunit and set the gain to what that is and nothing else LEAVE IT THERE, the gain isnt a volume knob for your amp its to get the amp and the radio on the same page (i.e. radios at 50% volume and so is the amp) if you turn it down too low that will make the amp very sensitive to volume adjustments and your amp will be at 100% while the raidos at like 50 or 75% and once you go past the 50 or 75 on the radio the amps going to keep trying to play higher even though its already maxing out which is going to cause it to clip and cause distortion untill it goes into protect mode. Hope this was helpfull to some one