What does the white wire do, and do the Smartphone Underbody or Interior Kits have an auto-on feature?Updated 7 hours ago

The white wire on both Smartphone Controlled Underbody and Interior control boxes is used for the courtesy lighting feature. When connected to your vehicle’s dome light or door pin trigger, it will activate the lights automatically when a door is opened—typically illuminating the kit in a solid color (commonly white) for entry/exit lighting. 

For auto-on functionality, there is a key difference between the two kits:

• Smartphone Underbody Kit:
  This kit does not have a true auto-on feature. It only supports the courtesy function through the white wire, meaning it will turn on when the door is opened but does not automatically power on/off with vehicle power. 

• Smartphone Interior Kit:
  This kit does include an auto-on feature. When enabled, the system can automatically power on and off when the white wire receives power from a switched source. 

In short, both kits use the white wire for courtesy lighting, but only the Interior Kit supports full auto-on functionality tied to a power signal.