No memory on stereo

I just installed a sony cd player in my father-in-laws 1973 Ford F-150.  Everything works fine except when he shuts off the truck there is no memory to the stereo.  I was kind of winging it with the wires since there wasn't an aftermarket stereo already in it.  Could someone advise me on which wires would keep the memory in the stereo--does it need to be constant or would that NOT shut off the stereo when he shuts down the truck?  Any help would be great, thanks.

Well you could find a constant 12v, and ignition under the dash. And ground the black wire behind the radio somewhere. Make sure you scrape away any paint.