Do you have an amp that just quit working? No sound? Here are a few tips you can use to see what's going on. If you are not 100% comfortable with performing these steps, you should have a trained technician perform these checks.
With the vehicle in park and the emergency brake pressed start the vehicle and check to see if there are any power lights ON at the amp. If there are no lights ON, start by checking all fuses. There should always be a fuse at the vehicles battery. If that fuse is OK, check to see if there are fuses at the amp. If all fuses check OK, then the amp may be defective and you would need to have the amp checked by a trained technician.
If there is a power light ON but no audio output, check to see if the RCA cables are securely seated in the amp. Also, check to see if the speaker wires are loose. If that all checks out, there could still be a problem with the input signal (RCA) or there could be a problem with the speakers or even a speaker wire. Some amplifier brands will have a power light ON and the amp could vary well be defective. If all of these checks out, you would need to have the amp checked by a trained technician.
GROUNDS, GROUNDS, GROUNDS. I can't stress this enough, bad grounds can cause numerous problems from complete system failure to intermittent output. If you suspect a grounding issue, remove the fuse at the vehicles battery and have the amps grounds checked by a trained technician.
If there is a RED PROTECT light ON, this means the amp is not happy. There could be a few things that could cause a protect light to come ON. An internal component failure, bad ground, shorted RCA cable, or shorted speaker wire. The quickest way to see if the amp has failed under these conditions, with the vehicle OFF, unplug the speaker wires and RCA cables. Then, start the vehicle. If the protect light went out, then there is a problem in either of these two connections. Have the amp checked by a trained technician. If the protect light is still on, with the speaker wires and RCA disconnected, the amp should be checked by a trained technician.