| The last diagram will work as long as you dont have a factory amplifier. If you have an amp, you can do the same thing at the amplifier. As long as you arent running a bucketload of power, you can use the stock wiring. D3ity is right, if you are going to keep the car for a long time, I would bypass the stock wiring and just run new. That way you know what you are working with, but the stock wiring is ok in most newer cars if your not comfortable in doing that.
One question, is your Alpine HU using the remote turn on lead (blue w/ white stripe) for anything in your current setup? I am just wondering if you have an amp in there and may not know it. You definitely dont want to run your new amp into the input side of your stock amp.
The crossover position is correct in your second diagram as well.
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