**Under Construction**
How to install an amp:
Amps are very easy to install. First of all, lets cover the wiring involved. In your typical set-up, there are only 5 wires/cables that come in and out of your amp. They are(in no particular order):
1. Power wire
2. Ground wire
3. Speaker wire
4. Remote Turn On Wire
5. RCA cables

Before we get to installing, let me explain a little bit about each type of wire/cable going to and coming from your amp.

Power wire:
Power wire is how your amp gets power from the car's electrical system. It is connected to your battery. There should always be at least one fuse on your power depending on your application. Some people do not run fuses but the people who do this are SPL PROFESSIONALS, it should never be tried unless you have a complete understanding of what you're doing. Not having fuses can destroy your speakers and amps, not to mention the possibility of your entire car catching on fire. We will go more in depth of fuses, distribution blocks, capacitors and batteries later on, for now, let us stick to power wire. Power wire varies in size depending on your application. After my limited years in car audio, here is what seems to be the 'norm' as far as how big the power wire should be for your amp(s). The size of the power wire directly varies with the amount of power your amplifier(s) draw. If you have a single amplifier, just pay attention to the RMS or continuous values of the amplifier. If you have more than one amplifier, then add the watts (remember, only use RMS or continuous values) and the sum of that is what you pay attention to. This is what I have concluded over my years in audio.
For up to 400 watts: 8 AWG
For 401 - 800 watts: 4 AWG
For 801 - 1200 watts: 2 AWG
For 1201 - 1600 watts: 1/0 AWG
While those numbers are no exact science, they are a good template to go by.
Do you plan on adding more amplifiers or replace the one you have with one that puts out more power than your current one? If so, get the power wire accordingly. If you have a 150 watt RMS by 2 channel amplifier right now, but are going to add a 500 watt amplifier and a subwoofer later on because you don't have the money right now, go ahead and get 4 AWG instead of 8 AWG. It is never bad to have larger power wire than you need. If you really wanted to, you could have 1/0 AWG running to a 50 watt RMS amplifier, granted the wire will not fit into the amplifier inputs. Having bigger power wire will allow you to upgrade later and will same you money and work because you will not have to buy new wire and you will not have to reinstall it. I will explain how to hook up two amplifiers from one power wire later.
Power wire can get expensive! And of course, the bigger the power wire, the more it costs. My FAVORITE source of power wire is www.knukonceptz.com . All the power wire in my truck has come from there. The price I paid for my 1/0 AWG was $2.25 a foot, that is extremely cheap! To give you an idea of how cheap that is, www.sounddomain.com sales Phoenix Gold 1/0 awg power wire for $5.50! A tip for everyone is that power wire is power wire. KnuKonceptz wire also has a higher strand count than Phoenix Gold wire. A higher strand count means more flexibility and when dealing with stuff as thick as 1/0 AWG, flexibility is needed! You also want to look for it to be oxygen free.

Ground wire:
Your ground wire is exactly the same as your power wire. You need to use the same size ground wire as you did for your power wire. This will eliminate ground loops and other potential noise inducing problems. The ground wire is 1 of 2 main places where noise from your vehicle's different components (like the alternator and starter) will get inside your audio system so it is very important to do it right. To make a ground, you need to find a place with no paint, just bare metal. 99% of the time you have to make your own. To make my ground, I pulled back the carpet a little bit and armed with a flat head screw driver, I began scraping a 1" by 1" square into the floor of my truck. After I saw the metal was nice and shiny, I used my drill and made a hole directly in the center of my nice, shiny square. After that, I put a ring terminal on the end of my 1/0 AWG ground wire. Then get a stainless steel screw and a lock washer and screw the ring terminal in the hole. Voila, your ground is done. Do not run your ground to your battery, it is a waste of money in terms of the extra wire you will need and it is also not as good as the ground I just explained.

Speaker wire:
Speaker wire goes from the channels of your amplifier to your speaker. The size of your speaker wire is like the size of your power wire, depending on how much power you'll be giving to the speaker directly relates the size of speaker wire. Again, I will tell you about what size speaker wire you need depending on how much power will be going to your speakers. These numbers are very lenient though. I'm a huge advocator of overkill, especially in speaker wire.
For up to 50 watts: 18 AWG
For 51 to 100 watts: 16 AWG
For 100 to 250 watts: 14 AWG
For 251 to 500 watts: 12 AWG
For 500 to 800 watts: 10 AWG
For 800 to 1000 watts: 8 AWG
Speaker wire is much the same as power wire in that it is all pretty much the same. Although the really cheap stuff can be quite crappy. The main thing to worry about when dealing with speaker wire is the shielding. It needs to be somewhat resistant to cutting and other hazardous materials such as grease that can eat up shielding on poorly made speaker wire after a while. Again, I recommend www.knukonceptz.com for all your speaker wire needs.

Remote turn on wire:
This wire connects from you head unit (a.k.a. radio) to your amplifier. This wire lets the amplifier know the head unit has been turned on so the amp will turn on as well. This wire is typically 20-22awg regular power wire. It is very small and can be found at Radio Shack or anywhere else.

RCA Cables (a.k.a. Signal cables or patch cables):
This is a greatly debated topic. Will the $9.99 ones work as well as the $99.99 ones? My answer to this question is no, it will not, but some might disagree. I recommend Street Wires ZN 3.0s or 6.0s. They sale for cheap at www.sounddomain.com/shop . The actual cable in RCAs are all pretty much the same. In reality, the main difference is the cable's shielding capabilities. Remember when I said the ground wire is 1 of 2 places that noise is most likely to come into your sound system? Well, the RCA cables is the other. That's why I recommend Street Wires. The connectors on the ends of RCA cables are the downfall of most. Street Wires takes extra steps to help prevent them breaking or inducing noise. Shielding, like in speaker wire, is also important. They too must be able to endure the harsh elements that a car endures such as grease and extreme temperatures. Remember, during the summer months, it is typical for a car's interior to be well beyond the outside temperature. In reality, a more expensive cable will not sound better, but they will last longer and are not as prone to induce noise.

Now that that is out of the way, lets move on to actual amplifier installation. Its very simple!
This is how to 'bridge' a single 2 channel amp. Bridging is simply taking 2 channels and making them one. It is done mostly with 4 ohm subwoofers.

First, mounting the amplifier:
While mounting the amplifier, it is important to take into account a couple of things. First of all, make sure that where ever you screw it to, you do not screw any other wires either to your amplifier or to any part of your car. This can cause some serious damage and can be quite costly. Second, amplifiers can get quite hot. Rockford Fosgate is notorious for how hot their amplifiers get. This is why we need to take into account space. Your amp needs to have a couple of inches all around it so it can cool itself properly. If not, you can fry your nice, new amp and no one wants that. To mount your amp, you need a drill. Find the screws you will be using and make sure the drilling bit is a little smaller than the screw. Find out where you want to mount your amp. I mount mine behind the back seat, you can also mount them under the seats or along the sides of the trunk in a car. After you know where you want it to go and making sure you're clear of all wiring, drill your first hole. After drilled, screw it in. Make sure your amp is level and drill the second hole. Drilling the holes on the top of the amp is usually better. Then screw it in. The bottom two are easy because you are not having to hold the amp while you drill which can be quite tricky. Now that its mounted, on to wiring it up!

Now, the power wire:
The amp I am installing is a Rockford Fosgate Power 550S 2-channel amp. It puts out 550 watts, so according to the template, we need 4 AWG wire. First of all, we run the 4 AWG power wire from the positive terminal on the battery to the power input on the amp. Since we are talking of a single amp application, we only need one fuse. For the particular amp we are using we need a 50 amp fuse. Never, I repeat NEVER install while your fuse is in the fuse holder. To put a fuse on the power wire, we need a inline waterproof fuse holder. The 50A fuse HAS to be within 18" of the battery. Here's a picture of my entire engine compartment. Its purpose was to show the dual batteries, but it does have the picture of my fuse. It isn't 4awg and the fuse is much bigger than 50A, you can still get the idea.

It is an ANL fuse. It is near impossible to find AGU fuses for high current applications. MAXI fuses are generally used for even smaller applications. To connect to the battery terminal, we simply take a ring terminal and put it on the end of the power wire and screw it down with the nut already on the battery post. Sometimes people (like myself) have problems with the nut working its way loose. Companies make special battery posts for amplifier connections that will not work their way loose. Here is mine, all it is is a regular screw-in side post bolt but with threads on the other side. That is where you can screw in your power wire.
From the fuse (that is within 18" of the battery!) we run the power wire through the engine compartment to a grommet in the fire wall. You should never have to drill a hole in the firewall, there should always be a grommet somewhere. Some firewalls are made with holes that can be punched out with a screw driver and hammer. I personally use the grommet that my steering shaft uses.
Zip tie your power wire to unmovable objects when running power wire through the engine compartment, the last thing you want is the wire getting caught in the fan or the insulation getting burned off exposing bare metal.
You then run the power wire along the side of your car to where your amplifier is. You can then cut off a piece of the insulation and shove it in the hole for the power wire and screw it tight. Rockford Fosgate amplifiers use allen screws to tighten everything down.

Next is the ground wire:
It is the same size as the power wire as I have mentioned before. It is best to keep it as short as possible. I already told you how to make your ground connection. It is connected to the amp in the exact same way as the power wire is. Here's an example of what a ground should look like before you screw it in.

Next we move on to the REM or remote turn on wire:
First, find the REM wire on the back of the head unit and either crimp or solder your extended REM wire to it. Run the wire under the dash and to the amp. On most amps, you must have a spade connector on the end to connect it to the amp.

Some amps are different, but for RF the power, ground, and REM are all on one side...we have installed everything on that side...so lets see what it looks like, the silver wire you see is the REM, the power, then on the bottom is the ground