Rearview Camera Setup, 2006 Volvo S60R

I know a little about electronics - enough to know how to solder wires, install home lighting and how not to electrocute myself. Circuits are a bit beyond me and hoping for some assistance.

Car: 2006 Volvo S60R

Headunit: Pioneer AppRadio II - has a input for rearview camera

Background: The car is setup to send a constant 5v to bulbs to determine if they're blown out. When setting up the camera, I wired it to get power from the reverse light and set the headunit to automatically switch to the camera when in reverse.

Issue: The camera would see the 5v feed and power up & the headunit would flip to the video feed but it wasn't enough juice to run the camera so I had 'green static'. I've added a SPST Contact Type Relay 4 Pin 30A DC 12V to the mix but it seems that it still sees the 5v and sometimes flips on - but not always. Most of the time it happens about a minute or two after driving. Not sure if the relay might be bad, or if it's affected by the 5v feed so I'm wondering if there's something I can install which would only power on the camera when it sees at least 12v and nothing less. Not sure if there's a different relay to use, or I need to add a diode or if there's some circuit board to add to the mix?

Thanks in advance.