My amp keeps turning on and off, have checked all

Is the main power wire going directly to the battery? does it do it under load only, or all the time.
Disconnect the RCA inputs and see if it continues to do it. if it still does it, then disconnect one speaker at a time, if it is still turning on/off with no speakers and no input, and has 12V direct from the battery, then it is faulty and will need service.
If it only does it under load, get a multimeter and check that the speaker wires are 4-6 ohms between them, also check from each speaker to body of car, there should be no connection.