Bottom line- you are not connecting the serial data between the 2 brands today (15 Jan 2025) because the components needed on the MTH side have not been released.
Mike wolf discusses that very adapter cable in this video https://youtu.be/m8dfVe890JY?s...OJoEP2Ohp2&t=553
The WTIU does not have the 9 pin serial data port of the past TIU.
The WTIU does not have a USB device port like the previous TIU that is an internal USB to serial conversion interface- again this is gone.
The WTIU ONLY has a USB host style port- and through testing of a pile of different brands and chipsets of USB to serial cables, haven't found a commercial off the shelf one that works.