There are a variety of different configurations that manufacturers use for the
B+ and ACC leads... most common that I've seen is for the deck to draw its main
power from the ACC (red) lead, and the B+ (yellow) acts only as a "backup"
supply to maintain radio station, EQ, clock, and other settings when the car is
off. Most of these decks will run fine without the B+ connected.
There are exceptions, however... a few still draw main power from the ACC, but
won't operate without B+ connected as well. Others use B+ for their main power
and the ACC is only a turn-on signal.
Would doing one or the other give me any control on switching it
on/off? There is a switch on the back of the ps, too, that I can use to
power on/off.
If you want to retain any stored settings, I'd say just connect the red and
yellow to the PSU together, and power it on and off whichever way is more
convenient for you. If you want to store radio stations or custom EQ settings,
just leave the PSU on, and turn the deck on and off using its own power button.
Pick up a cheap HDD-power Y-splitter and attach the deck power to that, then you
can just plug it into the PSU "properly" 
Sweet, the above makes sense, about the main draw and reserve power,
and I'll look into the Y-splitter.
Thanks again.