No one I've talked to can give me an answer, so I'll put this out here:

With the car off, will backfeeding voltage into the under dash fuse block through any of the circuits cause any problems? My intuition tells me no, but I'm not certain.

What will happen? Will the entire panel be energized? If the car is off, then there is a disconnect at the ignition switch, right? No harm to vehicle electronics or computers, right?

 

You won't damage anything electrically, but depending on what circuit you will be energizing could cause things to activate, such as windshield wipers or starter or something else that moves. So where your fingers are could be possibly dangerous.

 

Thanks, Dennis. Here's what I'm doing; Note the LED switch near the relay. The LED switch hot lead will be connected to the same pole as the under dash switched power lead for relay operation. This switch is for keyless operation. This is where backfeed to the dash fuse block will be sourced from when the car is off and I power on my electronics fuse block via LED switch and relay:

 

The diode was just an idea. If it isn't necessary, I won't use it. I believe there is an empty, unused circuit in the under dash fuse block that I will use, so I won't have to piggyback off another circuit, e.g. cigarette lighter, radio circuit, etc..

 

If there is going to be back flow, I believe in using a diode instead of taking chances. Nissan has done this in several different spots in your car.

I have to admit I don't fully understand the diagram you posted. The main thing is exactly where will you be tapping into to get the power. I see that one line along the bottom is labeled as 25 amps. This is too much amperage to pull from the fuse block in the dash. But if leds are all that will be drawing power from the under dash fuse block, then there will not be a problem.

 

Thanks, Dennis.