I hear that if you have more than 3 amps you should have a relay, Need to know how that would work?

I am going to have 4 nonfactory amps and one factory amp in the car. I now use a switch to turn the radio on and off and have two other switches to turn on the amps I have in the car so I don't have to kill my ears all the time I want to turn it up. I wired it up so the amps still will not turn with out the... show more I am going to have 4 nonfactory amps and one factory amp in the car. I now use a switch to turn the radio on and off and have two other switches to turn on the amps I have in the car so I don't have to kill my ears all the time I want to turn it up. I wired it up so the amps still will not turn with out the radio being on. How and why would I hook up a relay? I have the factory amp on the front speakers, one on the back, one on the 12" and one for the 2 10" and have one more amp that I am going to put in so the 10"s have here own amps. You can see in my pic that I made a fiberglass box that replaces the back seat. and does that set up mean that I have a WALL in spl comp rules?
Update: hi Akiyoshi A, do you work for google, I asked on yahoo. google was no help. and couple of people I know know the answer on yahoo and am only going to trust them
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