Originally Posted by voided

Good question, I just went through this myself about 2 weeks back:

You'll need 2 power wires for this setup. The first is for the camera itself - this can be either the orange wire from the trunk, or an accessory power (i.e. amp activation). The second power wire is for the lead to the back of the head unit - this one NEEDS to be the orange wire, because reverse activates "backup mode."

Personally I spliced into the orange wire and split it two ways, one to the camera and one to the HU.

Hope that helps.