First off you need to look at the wattage on your amp. Based on the watts you need to find a amp installation kit. If the 1250 refers to the number of watts then you should get at least 4 gauge wiring, but 1/0 gauge would probably be the way to go. Once you get the kit you have to run the wiring.
How to run the wiring:
First you are going to want to connect the power wire(typically the thick red wire) to the positive post of your battery. After that your are going to have to find a way to get the wiring into the car. With mine I went through the firewall, but the easiest way on the smaller cars is to run it through the fender. Once the wiring is inside you should try your best to hide it all the way to the truck. If you want to get professional with it you can run it under the carpet, if not you can run it under the little strip of plastic at the bottom of the door. If you do run it under the plastic be careful when screwing it back in, if you run a screw through the wire it will cause it to have a short in it. Once it is hidden all the way to the trunk you can leave it alone for a while.
Now you will have to run the remote and RCA cables, but to do this you have to have a CD player or radio installed. To install the CD player you need to go to a place that sales car audio and find a plug that will fit your car. If you find a place and tell them what kind of car you have they will be able to give you what you need. When you get the plug hooked into the stock wiring harness you can match and connect the wires by matching colors. Now that you have hooked up your CD player you can run your remote and RCA cables. If you look on the back of the CD player their should be two red and white holes, as you would see on your TV, to hook the cables up to. Once you hook them up you now have to hook up the remote wire. To do this you will need to look at the wiring diagram for the CD player and find out which color wire is the amp wire. You will have to strip the remote wire and connect the two. Now that you have them connected you HAVE to run these two wires down the opposite side of the car the same way you did the power wires. If you run the RCA and power together it will make all electronic sounds come out of your speakers.
Now all 3 wires should be in the trunk and ready to hook up to the amp. If the amp is over 1000 watts I would recommend a capacitor which will keep your battery from dying and lights from dimming every time the bass hits. I haven't hooked up a capacitor yet so I'm not exactly sure how but it should come with instructions. Now you should have your amp hooked up and all you have to do is hook the speakers to it and it should be ready.
I know it's not organized, but hopefully it helps.
If you have anymore questions then feel free to email me
