So I just recently installed a 1500wrms sub pushed by a 3000wrms amp, in my '04 Grand Cherokee. I only use a little under 20% gain from the amp, and it does dim the lights pretty good if I really let it bump. I plan on doing the big three upgrade before I upgrade to a high output alternator. But I was curious about just how high output I could go without frying any of my electrical system. I also looked at other threads for some research first, and in doing the big three, seen mention of also upgrading the fuseable link, and something about the headlight relays, which I didn't quite understand.
Thanks in advance for any helpful tips or suggestions.

What is the "big three upgrade"?

Calculate your load/ draw requirements before upgrading your alternator. The stress is on the alternator if it’s unable to supply adequate amperage. Voltage is regulated at a nominal constant of 13.7 to about 14,0 volts, and shouldn’t increase much past that unless there’s some malfunction with the alternator. Proper wire gauge is as critical as a higher output alternator in order to be able to supply your accessories.

I'm in the process of figuring out the load that is on the alternator. Think I'll still go ahead and upgrade my power wires under the hood, and possibly install a four farad capacitor, and see where that takes me. I figure if I upgrade to larger gauge wire, and a capacitor can keep the volts at a steady 13.6, then I really shouldn't have to upgrade to a high output alternator.

Which wires?

Lots of people make the mistake of thinking that running an extra load like a winch or a big amp means that they need to upgrade their starter cable and the main ground cable. Nope. They don't have anything to do with it. You might want to upgrade the wire from the alternator to the battery, and you certainly want to upgrade the battery to body ground and the grounding point (it's wimpy), but the starter isn't suddenly going to start drawing more current just because you have a winch or a big amp or a bazillion off road lights.

This might be what you want

Thats what I have. Works good.

Same here. It's a great upgrade.

I have one too and it works great. I use 4ga battery cable off the alternator

Yeah, that's what I did. Upgraded/augmented the positive cable from the alternator to the battery, and battery ground to chassis with 0 gauge wire. Plus upgraded/augmented the engine to chassis ground with 5 gauge wire.

Would be great if 250 amps would be enough. But for the power I am pulling with the sound system, plus the things that normally run on the alternator, plus any future upgrades, I have determined through research, that I will need at least a 320 amp alternator. The one I'm looking at is fairly salty, but will be worth the expense in the long run.

Go with the 250 and a 2nd battery. Your gas mileage and power will thank you for it.

Power from an alternator isn't free. It's taken from the engine. Bigger load on the alternator, bigger load on the engine, which translates to more fuel to move the vehicle the same distance, and less power available to move you down the highway.

That's a waste of copper. You don't need anything near that big for that short run. It may impress people who don't know any better, but that's all it's doing.

Normally it would be a waste of copper. I knew when I did it, that it was a little overkill. But the wire was left over from the install, and was too short for any longer run use. It was actually perfect length for the application, didn't have to cut at all. Such is the beauty of planning out materials.
And I would tend to agree with going with the 240 from mechman. It would indeed take more hp and gas to turn the 320. And through continued research, I am finding that it's most likely inevitable that I'm gonna have to go with a second battery, no matter which amp alt I went with.

It hooks directly into the winch connections. And yes, you need it on a tough pull when the Warn winch, which can pull 800 amps is really pulling down. I was glad to have it then when I was hung up on some rocks