We are talking about and testing 2 different circuits.
In your video, your are testing the "consumer switched off" wire/circuit (red with black stripe).
On 1997-2000 986, the ground is switched for the courtesy lights (door and dome). On 2001-2004, lights were added (footwell, door handle). So for later models, the dome light and door lock light still have switched ground, but the footwell and door "orientation" light (whichever that is) has constant ground and positive is the "consumer switched off" red wire with black stripe. The consumer switched off circuit is deactivated after some time after ignition is shut off and door closed if car is not locked, or immediately if car is locked, so it has a switched 12v+ controlled by that circuit.
So, you can tap into the "consumer switched off" circuit for a switched 12V+, but it will shut off as soon as you lock the car. I don't know how long it stays on if you don't lock it.
If you want the circuit that slowly dims out, that's the dome light/door light circuit and is the switched ground (brown with yellow stripe).
https://m.youtube.com/watch?v=Peyh1sV0Hbo