I was surprised to discover that the MAF wire goes hot when the ignition is turned to the Accessory (first) position. Found this out because I was monitoring intake air temp (sensor is part of the MAF) and noticed it started climbing as soon as the key was turned on. Of course once airflow starts, it cools way down.

If you turn the key off, as you all know the accessories (radio, windows, etc) continue to operate for a short time, (or until you open the door), and under that condition the MAF does turn off.

Why do I care? Just that sometimes I'll listen to the news or whatever while sitting there with the engine off, now that I know other engine related electronics are also "on", guess I'll just cycle the switch back to "off" as required.

 

Yeah, my dad always told me that's why you don't want to leave it "on" when listening to the radio only. I know older cars have an accessory notch if you turn the key the other way, that's meant for just the radio or things like that.