Headunit power help

Alrite... i had this problem when i was hooking up my friends head unit. There is i dont remember what its called... i beleieve its for constant power to go to your system it should be a yellow wire. if you dont have that hooked up your wasting your time. what i did was connected it to the power wire and my headunit worked perfectly but the problem was that it never saved our features eg. the time so what i believe you do is run that yellow wire straight to the battery and it should work fine