I have a Response 4 X 100 watt RMS amp, and when hooked up correctly the protect light still comes on when i power it up. I replaced the amp with a friends amp and it works perfectly so it is nothing wrong with my wiring. Is this a common problem with amplifiers? and how can i fix it???
It's likely that the output transistors failed. That's the most common cause for an amplifier to go into protection.
With no power applied to the amp, set your meter(hopefully you have one) to ohms and measure the resistance between the terminals of the output transistors. You should find none that have anything close to zero ohms between any of the terminals. If you find one or more that have ~0 ohms between terminals, they need to be removed from the circuit and checked. If you have several in parallel, it may seem as though the entire group is shorted but generally one fails and the others are OK. Of course, when you have one defective transistor in a group of parallel transistors, you must replace all of the transistors in that group.
Open or broken emitter resistors can cause an amp to go into protect. If you don't find any shorted outputs, make sure there are no broken terminals on the emitter resistors.
Of course, the amp is a cheaper one, so it might not be worth all of the testing.