join the red and yellow allong with the power cable to the stereo. This will not only allow you to save the memory, you'll also be able to listen to the radio while the car is completly off with no key in the ignition.
Another thing, just maybe, you might be losing the memory because of the battery not having enough of a charge, it might be old, that used to happen to me until I got a new battery.

Will work for parts...