Battery shutoff switch/radio presets

The main radio power is separate from the memory power so I can't see any reason a single dedicated line to just the radio memory will energize anything else. I also don't think you need a diode to isolate it. If you do decide to use a diode the anode is what gets connected to the battery positive the and the cathode (end with the stripe) goes to the radio. Only thing is you mentioned the 1N4000 series and using a 5 amp fuse. I think the 1N4000 is only rated at 1 amp. A 1N4004 is good for 2.5 amps. That's the limit of my memory on them. I have a Sylvania book down in the basement and can look up what it'd take to handle 5 amps but again I don't see why you'd need one.