I was looking to install the PAC-SWIPS. I was looking that the instructions and it said to hook up a 12v accessory to the white/black wire on the car harness. Anyone know why? The pinout says the white/black wire is a 10-Volt Reference

 

The stock head unit would supply 10v to that wire so it can compare it to the wheel control output and determine what button was pressed. Since the stock head unit is no longer there to supply this, the PAC compares the difference between the 12v from accessory wire, and the button output. The voltage is just going across resistors (that dont care about the 2v difference)in the wheel switch network.

Be thankfull that's as far as the complication goes. Some make/model cars you haveto wire in resistors to the switches too. that's why there are a bunch in the PAC package.