I got too tired of having all my settings on my upgraded stereo unit lost every time the battery was disconnected. I found out that the HU kept the presets when it was disconnected by removing the connecting cables, but not when the battery was disconnected. so... I installed a small rectifier on the Constant (blue) wire that is on the hu harness. You can easily test for 12v either using a test probe or a meter and find the only pin that still has 12v when the key is off. (Its next to the gray wire on the plug with the most wires to it.) I cut the blue wire about 2" away from the connector and installed the diode with the cathode end (has the stripe) to the wire that goes toward the hu and the other end toward the wiring harness. I used heat shrink tubing to insulate the connections. I disconnected the battery after the hu was reinstalled for over 45 minutes, and it still had all the presets intact! I also have a welcome screen and sub settings (which are humbug to re-do) so I am quite happy with not having to do it again, each time the battery is taken out. Since the head unit has a system to keep the memory alive, I figured when the battery was removed, the rest of the car's electronics was bleednig the power out, and now the installed diode prevents this from happening. Cheap and simple mod, and quite effective!