How to modify 12V alternator to produce 16,8V?

By the way, I just got my very first client after bringing one of my stock speakers I had laying around into school and was showing people how speakers fundamentally work (with the good old battery trick), and then I salvaged an aux cord I had laying around and cut it open and connected my phone directly to the 6.5 inch speaker via the left channel positive going to the positive on the speaker, and the ground to the positive. And it worked, and albeit a little quiet (probably same volume as my phone's built in speakers), up close it actually sounded pretty good... Anyways I digress, but a girl asked me if I happened to know how to play music from her phone into her car radio, and so long story short, I'll be doing my first install for someone else (for free of course, I'm a noon, and she's a friend and kind of cute anyways). So far she just wants a new head unit which should be no problem. 2006 Hyundai Sonata with 6 speaker configuration. Did some research on Crutchfield, found the right single din bracket, the wiring harness, and that's all great.

A couple of quick questions; Solder (and then electrical tape?) or crimp the harness from Crutchfield and the connector that comes with the radio? In my car I crimped because I needed to tap into the speaker level signal from behind my stock head unit (from the stock connector) and wasn't comfortable soldering inside my car on tiny little cables.

Using the correct adapters and a compatible head unit, how hard is it typically to integrate steering wheel controls if that's something she decides to keep them? Where do I find/connect the wires (behind the radio?)? I'm generally a pretty good problem solver but I don't want to go into this completely in the blind.

Any tips on doing a clean install? I'm considering just telling her to come back when I say, as I can imagine some people would start to sweat watching someone else who's uncredited, unscrewing and popping panels out...

Lastly, I have purchased and installed an aftermarket head unit in a cooler and put a 130ah golf cart battery, 4 jbl 6x9s, a cig lighter outlet, 2 usb ports and a voltmeter all in it. But for the head unit I just had to cut a hole with a jig saw in the side of the cooler (which is the ultimate tail-gate or party boombox BTW, I can charge 7 phones at a time and play music at full volumefor 30 hours straight before my voltage drops below 12 (at which point I recharge)), and it came with a metal sheath to be put around it... So for putting a similar head unit in a plastic bracket for a car, is this correct? This is presumption mind you... Take the plastic bracket and the metal sheath, put the metal sheath in and bend the corner/tab things up so that it stays in place, take the wiring connecter through the plastic bracket and metal sheath and plug it into the head unit, snap the plastic bracket in place, and slide the head unit all the way in? And then put the dash back together and call it a day?

I have already watched a video and looked up step by step how to remove the panels and the radio in her car, to be sure I don't break anything.

Thanks for the help mate!

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