the door ajar light remains on with doors closed

One or more of the door latches are bad. The switch to turn off the dome lights are built into the latches. You can try spraying wd-40 or pb blaster into the latch openings and shut the doors quite a few times and see if the light goes off. It's a temporary fix. At least the light will be off and you will know which one is bad. Start with the drivers door. It's either that or you turned on the dome light switch on the dash or a button near the dome lights.