I've got an 04 blazer. Currently running less than 1k in ca audio. However, I plan to run more than one amp and add subs into the package, nothing more than 3k watts. Should I purchase a HO alternator and Upgrade the wires? Or is adding a 2nd battery enough. Any input would help a lot before I go make a purchase I don't need.

 

A second battery only adds more capacity, not generation. So if you listen to the system for a long time at high levels, you'll kill your stock alt, and drain both batteries. An upgraded alt is a better purchase than a second battery. If the alt has a hard time, then get a second battery.

For the original question, yes, definitely do the big 3 if you are pushing that much power. Stock wire size is like 6 or 8 ga.

Here's a chart on wire size vs amps vs length


3KW @ 12V = 250A

Depending on if you are talking RMS or peak, you should have larger wires either way. Fire = bad