i am aware that this is a common problem that people have suffered, and i am not just repeating an old thread. the problem is that other threads havent resovled this. i have done my research however i seem incapable of wiring my cd player in a way that causes the unit to maintain memory

the car is a 1990 ford fiesta
the unit is a sony cdx-gt210 xplod drive-s mp3 wma

if i wire the ground (black to brown), live (red to red) and constant (yellow to yellow) the unit powers up but it doesnt have any memory, i have also tried other combinations of this, sometimes it powers up, sometimes it doesnt but it never retains memory!

this is really frustrating me and any help offered would be much appreciated!

many thanks