I never noticed this befor on our cars and I don't think I've ever seen it befor on any of my other cars. The lid of the odb port has a resistor and 3x prongs on the opposite side that plug into the port.. what is this and what's its use ???

 

Off hand I'd say if those 3 prongs fit into the OBD2 port connector it is some means of letting "something" know the lid's closed and nothing is plugged into the port.

Supposedly my BMW will sound an alarm if something is plugged into the OBD2 port when the engine is shut off. I have not bothered to test this and I have not bothered to check if there's a lid/cover for the OBD2 port.

Nor have I bothered to check my 2023 MINI's OBD2 port.

I used to run trip/data loggers in my vehicles but so far I have not bothered to put one into either of my current cars.

 

that's why I found it. I plugged in my x60 gauge. It almost looks like something may have attached to the outside cover and it provided power to it , just my guess.

 

When researching it in the past the answer that made the mosr sense was that the cover was a shared part with BMW. Some BMW’s had an additional round 20 pin diagnostic port in the engine compartment and the port wouldn’t work unless the OBD cover was closed.