A car amplifier will need a remote wire connected, to the blue remote wire found on the car head unit's wiring harness, in order to power itself on and operate. This is because when your turn on your car stereo, it sends a small voltage down the remote wire line, to the amp to power on, so without it connected to your car amplifier, it simply won't turn on.
1) Before you go an buy a separate remote wire, check if there is an remote wire in the middle of the RCA cables you are using with your car audio system, the wires that send sound input signals to your amp. Most RCA cables from good leading car audio manufactures like 'Rockford Fosgate', JBL or Autoleads, have a remote wire in the middle of the signal leads, which is convenient, as you don't have to buy another wire and run it down your car. However if you are using a cheap, poor quality, unbranded RCA lead, then you are very likely to not have a remote wire already, so you will have to buy it, but check, just in case it has it.
2) Next look on sides of the car amplifier, to find the 'remote wire' terminal, it will be labeled, so it shouldn't be hard to find.
3) Once you have found it, then get a correct sized and shaped screwdriver and unscrew the screw, in the remote terminal.
4) Once you have done that, then get a 'wire stripper' and strip of 1cm of plastic insulation coating from the remote wire. Then insert that wire into that terminal, making sure all the wire braid is fully in and then using your screwdriver, screw the screw tight, to ensure an secure connection.
5) So now the remote turn on wire is connected to the car amplifier, now you need to connect it to your car deck. This is simple, remove your car head unit fascia trim, also known as 'surround', from your car's dashboard, then using din tools or by inserting a flat head screwdriver, to pry it out, be careful not to scratch it!
6) Once it is out from its cage, locate the wiring harness, its a plug that goes into the rear of the deck, with lots of different coloured wires coming out from it, speakers, power, ground etc.... The wire that you want to locate is either a blue and white colour or on some decks it is an blue wire, it should have an paper label on it, saying something like 'remote turn on'. If you can't find it, use an user manual, for the make and model of your deck to make 100% sure if an remote wire actually exists, and if it does exists, find out correctly which wire it is, as it may be coloured green or orange, depending on the manufacturer brand. Finding out correctly is vital, to prevent damaged to the amp, by sending a high voltage signal to it, if using the wrong wire.
7) So when you have found the correct wire, now what you need to do is, using your 'wire stripper', strip of 1cm of plastic insulation coating off the wire, to expose copper braid. The remote wire on your car stereo, might be taped of, with insulation tape and may not have any braid at all on it, if this is the situation, then remove the insulation of that wire too.
8) Hold both remote wire's copper braids in your hand, then gently, twist them together, until they are tight and secure. Then use insulation tape to tape up the exposed copper braid.
9) Then push all of the wires, of the wiring harness to the back of the din slot and slowly place the car head unit back into its cage and replace the fascia trim, you removed earlier on. Once you have done that, put your key into the car's ignition and start up the engine, then stereo will power on.
10) Insert a CD and play a track, which track it really doesn't matter, it is for an test. Then open the trunk, look at the power light indicator on the amp, it should be lighted up, to show it is powered on and is working. However, if it is not working, check if the ground wire is connected to an solid ground.