an amp is quite a bit more involved. Not terribly difficult, but usually fairly time consuming.
You'll have to run a 8 or preferably 4 ga wire from the battery to where ever the amp is going to go. Getting it through the firewall is usually the tricky part.
You'll need to fuse that wire within a few inches of the battery (50-80A depending on what size wire you go with).
You have to find a spot near the amp to make a good chassis ground with the same size wire as power.
You have to run a small remote turn on wire (16-18ga)from thehead unitto the amp.
Then you need to get signal to the amp - whether that be through rca cables from an aftermarket HU, a stock amp delete harness from your stock HU, or a line output converter connected to your stock speaker leads.
You will probably need to run some speaker wires as well - that would probably be easier than trying to locate a spot to splice into the stock wires.

 

wow that looks a lot more complicated than i thought it would be

 

Its not that complicated... maybe an hour or so max.

 

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damn, you must be good.

 

Also look into upgrading your chasis ground at the battery. This will help to resolve a lot of the dimming light issues caused by an overdrawn alternator. All it takes is running a new string of 4awg wire from the negative terminal to the chasis. I honestly wouldn't look into upgrading the alt. if you're running less than 1000 watts between all your amps.

 

How would i run the wire to my chassis?

Sorry for the questions, not really expierenced at this and dont have much money, so im trying to learn as much as i can to do it myself.

 

you can usually find a bolt somewhere near the amp that goes into a sizable piece of metal. The hang up is usually paint/dirt/debris that prevents a good electrical connection. Some solvent andsand paper is all you need to fix that.
I used a bolt through one of the cargo tie down loops. I didn't even prep itas well asI should have, but it worked fine.

 

For the chasis ground at the battery,you'll need a piece of 4awg wire, roughly 6" long. Find a good solid bit of metal near the battery tray and using sand paper or a wire brush of some sort, clean off the paint and any debris. Use a self tapping screw and a star washer to secure one end to the bare metal surface, the other end to the negative battery terminal. This is the easy way to go about it, but if you have access to the wire that is actually grounded to block, replace that whole section with a thicker guage wire. Mine unfortunetly rant 80 different directions and grounded somewhere around the transmission or underneath the intake manifold, and I didn't feel like ripping it all out to replace a wire. I did option number one and it has all but eliminated my dimming problem. Only when I blast it do the lights begin to dim, and even then it's only just a tiny bit.