Re: no power
I'm not familiar with the grand marquis, but if the switches are on the door, u will find that the switch that locks out the passenger controls has a broken wire.
It is probably broken in between the door and the door frame near the hinges. From opening and closing the door.
I had an 82 Fairlane that had this issue, it was a pain and it seemed that as soon as I fixed one wire another would go the next day.
I got sick of it and got rid of the car. But that's just because I have no patience for such things. - lol