Here how to tell if the head unit is pulling power even when off.
You need a 10mm spanner for battery and a multimeter.
Set multimeter to read amps (see the meters instructions, if you're unsure how this is done, stop reading and don't try this, at the very least you'll melt the multimeters wires fit you get it wrong)
Switch everything off, alarm, lights, boot light, head unit etc,
Remove negative terminal from battery, have alarm fob to hand as it may trip alarm.
Connect one end of multimeter to neg terminal on battery and the other to the neg clamp you have just removed. This again may trip alarm, turn if off again. if you get a minus reading, swap the ends of the meter over, so the one you were holding against the battery is now against the clamp and vise versa.
Take a reading. A reading of 0.02 to 0.04 is ok.(the clock)
If you get a reading of something like 0.45 you've got a drain.
Now if you have a high reading, remove and unplug the head unit and take another reading, has it gone down to 0.02 or 0.03? if so, the head unit is drawing power even when off and will flatten your battery in a few days, you need to find a switched live to connect the head units red wire too.
If you disconnect the head unit and it's still drawing the same as before, you've either got a drain somewhere else, or somethings still on, recheck everything and start again.
A modern head unit will usually need two power sources.
Red wire from the head unit is the switched live, ie, goes dead when the ignition is switched off (we don't have this switched live in the cars loom, you need to fine one under the centre console, flip out the gearlever trim, it's an orange wire down there, disconnect head unit's red wire and splice it into the orange one)
Yellow wire from head unit, this powers the head units memory for stations etc.