No need for the yellow wire to be connected.
After trying to find a fuse to tap and even connecting the yellow wire directly to the battery but I still couldn't get my e88 to sleep.
I got this from
https://forum.xda-developers.com/and...w-e90-t3800052
Settings
scroll down to factory settings
password:126
***Change this seting***default power status;
memory of last status
apply
exit
yes to reboot
This saves the stations in memory. The clock will updated by GPS automatically within about a minute. If you don't mind the head unit rebooting every time you drive the car (takes a about a minute for me) then there is no need for the yellow wire which I tested and draws .05 amps while sleeping and .3 amps awake.