2004 Explorere limited HU replacement

First post, long time lurker and I posted this in the wrong place - duh. So let's try again.

I found a lot of useful info on here already but ran into some interesting issues while trying to replace the 6CD Audiophile head unit with an aftermarket DVD/GPS/Camera/Radio unit off ebay.

First issue was the main harness carried the single yellow Steering Wheel Control wire to pin 18 but the Metra harness lacks a pin in number 18, so I will have to splice in the AXXESS AWC-1 onto that lead and take a 12v switched from the Power Antenna lead which is not used in my application.

Second was that the METRA Sub woofer mini harness had two RCA connectors plus two blue/white power on leads and all were in the wrong spots. The el cheapo ebay HU has a single SUB RCA input which is fortunate because the Ford sub has only a single pair connecting, so I carefully removed the pins and fitted one RCA into the appropriate spots on that connector.

Third was that the Sub Power On is 5v out of a stock unit and 12v out of the replacement HU, so I need to rig up a 5v feed. I tested it with a USB charger and that works but I'd like a more elegant solution and wonder if there is a 5v feed conveniently accessible under the dash or do I need to install a voltage regulator to the existing 12v poweer on lead?

I picked up a 5V voltage regulator from Radio Shack and soldered that close to the back of the Subwoofer socket and connected the input to the HU power antenna output. I will test it to make sure that I have a constant 5v output to keep the subwoofer on and then back to the AWC-1 wiring