Spray WD-40 on all door lock jams including the rear gate door. Problem Solve...
___________________________________________________________________Get some dry powder lubricant, like graphite, and go around and lubricate all switches - don't forget the rear gate. This happens occassionally on my 1998. Same problem.
Put a new switch in the door.
I would hope that with a '03 you would have some warranty to fix this. However, in the door jam of each door on the vehicle there should be a push button switch. When the door is closed, it would push the button in opening the contacts within and stopping electricity from going to the dome light and dash light. Check each switch for one that looks visibly damaged from something being slammed in the door. Close all the doors and then one at a time, open one door and manually push the button all the way in with your finger to see if the light goes out (maybe the door just isn't pushing the switch in far enough). In one years time the switch shouldn't be worn out. There could be other things that would cause this but the switchs are definatly the easiest starting point. Might also want to look at all your fuses.
I have an '03 that has this problem. Unfortunately though, the previous answer doesn't apply to the 03 expi--there is no "door closed" trigger, the latching mechanism supplies the car's dash light with the information as to whether the door is closed or not.
I was counting on a mechanical problem with the latch and narrowed it down to the passenger rear door. I gave the latch assembly a good coat of WD-40, closed and opened the door a few times to work it in, and it works fine for about a month or so. Then you spray in some more and hope the magical elixir of WD-40 works again.
OK I guess I should contribute since these forums have helped me in the past. This is apparently a persistent problem with 03 Expeditions. Don't know about other years.
Problem is a sticky door ajar switch sensor on the door latch itself inside the door. These particular switches are poorly designed and use a brass plunger in a white metal body. When moisture gets to it over time, the white metal body of the switch corrodes causing the brass plunger to stick in the depressed or open position which makes the electronic control module think the door is ajar when its not. Spraying WD-40 in the latch mechanism where the switch is located may work for a bit but when the WD-40 evaporates, the switch will stick in the open position again causing the same problem. The best solution is to buy a new switch and put it in. You can try and recondition the old one - I did but I don't know how long it will stay OK. The switch is located on the inside of the door mounted on the door latching mechanism. You have to take the door panel off and peel away the insulator plastic to get at it from the inside. Remove the latch by removing the 3 torx screws that hold the latch in place. You will also need to disconnect the door lock and door handle actuator rods that are connected to the latch to allow you to move it up to the door opening so you can work on it. The switch has a 2 wire latched connector attached to it. Remove it. The switch itself has an orange plastic housing and is easy to recognize. The switch comes off by twisting it clockwise to release the snap connection. You will notice the brass plunger is stuck in. Best fix is to replace it with a new one. If you want to try reconditioning the old one because the dealer will want more money for a new one than the truck is worth, than spray some WD-40 on the plunger and wait 15-20 mins for it to penetrate. Grab the brass plunger tip with pliers and pull it out. Push it in and out till it moves freely. The plunger is spring loaded so if its loosened up you only need to push it in and it should pop back out on its own. If you want to verify the switch is working correctly, use an ohm meter. Plunger in is open. Plunger out is closed. Once you have loosened up the plunger and the switch is operating correctly, use white grease or lithium grease on the mechanism and switch to stop any future corrosion problems. Good luck.
Note: The switch comes off turning clockwise on the driver door and counterclockwise on the passenger door. Thanks for this very helpful information! dovogt 3/19/10