In my 1992 F150 i have a newer cheap stereo from walmart.. if the truck is off for like 5 min it will factory reset. it really has me stumped and making me mad. did some research on here and they said that the 12v constant wire is hooked up improper. which could be, but this just started happening after a replaced my alternator. any help would be appreciated.

 

There might be a separate fuse in the constant or memory stay alive wire which blew during the alternator swap. Maybe check that?

 

I'd pull the radio and double check all the connections also. There may also be an in line fuse on the radio wiring itself to check also.