Transmission stuck on fourth gear and speedometer fluctuates vehicle stationary

Hi,

Audi a8 1998 Quattro, automatic trasmission jumps up to 4rth gear and stucked at 4rth when vehicle is stationary at traffic until the engine is turned off and on, also speedometer flactutes at vehicle stationary (check video)fault codes at transmission are p0721 and p0703, I like the know the location of the transmission output speed sensor and it's wiring diagram, also want to know how to trouble shoot the fault code p0703, my brake lights are working properly, when the faults erased after test drive they appear again.
Thank you.