Help with Double DIN conversion

[Jamesp]

So it is in, and sitting in the driveway it works great. Problem is, when the car moves it shuts down. Very predictable, drive at a crawl, less than 5 mph, and it works. Gently accelerate to anything above that (forward or reverse) and it turns off. Does the Boxster cut power to any radio lines when the car starts moving? There are certainly many more wires to the original head unit than the aftermarket.