I'm trying to power an arduino uno from the teensy at Vin and GND to teensy 5v and GND, but I'm not getting any power,

when tried powering the arduino and leaving GND connected to teensy, the arduino is powered but no readings at the teensy, do I need to connect also RX from arduino to teensy TX for serial to work ?

Any ideas or connection diagram possible.

I'm using a voltage divider of 1.66K ,1K between the TX and RX on teensy