Hardest part IMO is running the wire through the firewall. I haven't been lucky enough in any of my cars to just use a grommet that already exists on any of my cars.
You'll need an amp wiring kit, use
this to get the correct gauge of wire for your particular amp and length of wire run. Most kits include all necessary pieces except the converter to give the amp the audio signal.
1) run your power wire from your battery back to the amp. Short as possible is the best and don't run it anywhere that it could get pinched and ground out. Ensure you have an inline fuse at most 12-18 inches from the battery. Before you connect anything to anything disconnect the negative terminal on the vehicle's battery and leave disconnected. You can connect the power wire to the positive terminal on the battery. Most amp kits have the parts needed.
2)Make a good ground connection back near where you are hooking the amp up at. Make sure you have a good metal-metal contact not just metal-paint contact the shorter the better.
3)Whenever I have a vehicle with no aftermarket head unit I usually run an amp turn-on from the fuse box. Do not connect it until right before you connect the ground wire back up to the battery in the hood.
4) I used a high level converter in my f150 and the quality was terrible. I recently used something I had laying around and was astonished how great it worked.
This is what I used and it did a great job in my sisters grand prix.
I tapped into her 6x9's in the trunk to use as the input since she insisted on her stock radio. It works great you just have to be careful when adjusting because distortion is what blows subs/amps. Where you get the signal is your choice and many will recommend different ways of doing it but it is working just fine in my sisters car.
5)I'd get a small/short run of rca's 2ft or less to connect the amp to the crossover. Chances are the amp kit you bought will have 15-20ft rcas so these will make the install cleaner.
6)Connect the power, ground, remote wire and rca wire up to the amp and crossover. Once everything is connected properly the only thing left would be to hook the turn-on wire to the fuse box (assuming you have the subs already connected) and then follow that by the ground wire at the battery. Before doing this though double check everything to see that you didn't cross anything or connect anything in the wrong spot.
Test everything out and see if the amp turns on or not? You should be good to go, if not check fuses and connections. I'm sure I missed something...
