in the ecu

Unless something isn't working properly, that is for an option your car doesn't have. You will find more of them around the car. In this case it looks like the connector for the ECU compartment accelerometer that CATS equipped cars have. Just put it back where you found it, it isn't connected to anything.

It's definitely for an option you don't have. I have the same empty plug. My guess is that it's for the center console phone that most of us didn't have.

thanks... that's what I figured but now I can ut it too rest

Out of interest, what part of the phone system is in the ECU compartment in the engine bay?

That is where the flux capacitor connected in rare “Back To The Future” models with gull-wing doors. Wasn’t a big seller, so Jag discontinued it.