Four Low light constant on, no 4WD at all

[VMX12R]

My sister has a 2004 Explorer and her battery died the other day and she asked me to replace it. After I replaced it she states that the 4 Low light is now illuminated and stays lit, but its not in 4 Low or 4WD at all. I drove it around the block and the 'Auto' 4WD doesn't seem to work either as I was able to easily spin the rear tires on ice and the front wheel didn't seem to kick in and assist. Of course, she believes that it was something I broke when I replaced the battery, so I promised her I would look into it. Pushing the 4WD control buttons doesn't make any changes and it would seem as though the 4wd is not activating at all. Pushing the 4 Low, 4 High and Auto 4 Wheel makes no difference and the 4 Low light stays lit. The lights are not flashing. I checked all the appropriate fuses, disconnected the battery for 10 minutes and reconnected and the Low 4WD light stays on and the 4WD doesn't work. I did a search on the forum and didn't come up with anything about this specific problem. Any ideas on the issue, or any other troubleshooting I can do to further determine the issue?

Edit: There is also no lights lit in the dash to indicate that its in 4WD.

Thanks in advance and Happy New Year!

 

[FordFool2]

Was just back in Omaha visiting family for the holidays.

You said you checked the fuses. Confirm that you checked fuses 8, 11, and 18 in the power distribution box under the hood.

There are 2 relays that control the clockwise and counterclockwise rotation of the transfer case motor. They are located behing the coolant reservoir against the passenger front fender. Relay 64 is clockwise, relay is 65 is CCW, and relay spot 66 is open.

Also check the wiring/connector down to the transfer case motor just in case she got hung up on some snow pile or drift.

Good luck.