on the 126 that flap is located behind the glove compartment.It is operarated by two vaccum actuators and i agree with ILUVMILS.
It does deactivate itself after 30 minutes.
If it cuts out real soon, it might be either the switch(most likely, as happened to me ) or loss of vaccum.-
Once I had lost vaccum because one of these vaccum lines had become undone at the switch. Real easy fix