12v goes to ignition.

Well.... I'd say that depends on how you want it to behave...

I have my +12V supply for my MkI wired to constant, not ignition.
I like to be able to use it w/o having to stick the key in, and
I won't leave it alone in the car long enough for battery drainage
to be a factor.

On the other hand I have my other headunit - tape&radio, which I
haven't used for ~3 months - wired as it is 'supposed' to be with
constand and keyed +12V. Will probably remove it now that the receiver
functionality improves on the empeg. I can actually pull in some of the
stations around here w/o any antenna connected, so despite the bad rep.
the tuner of the MkI has, I think it'll work good enough for me...
...until I give in and buy a MkII...

/Michael