I can't believe some of the things coming from a certain member on here. fixinit.
1st of all, what does high mileage have to do with electrical charging wires, aka big 3? Nothing. What does the age of the vehicle have to do with the big 3? Nothing. You gonna not do a tune up on a vehicle because you feel it's not needed? No. And why is because that's part of reg routine maintenance and to keep the car running good. Ignore it and problems may occur later on down the road. Getting off topic but had to throw a pointer out there.
I would love for you to attend a few stereo competitions hang outs or db drag...whichever. Ask ANY car audio enthusiast. They will tell you that adding anything audio to an existing vehicles electrical system will require beefing up the electrical. It's been known. Google will confirm this, as well as anyone in this hobby. The vehicles big 3 wiring is just to get by on STOCK electrical, heater, A/C, dome lights, starting the car over, stock radio, etc. It does NOT matter the age of the vehicle nor the mileage.