4WD Dodge

Hi, I have a 99 dodge 1-ton. Just recently we had a snow storm had to use the 4wd now when I drive in 2wd the 4wd light on the dash comes on sometimes or just flashes then goes away. Can you tell me what could cause this? I have used the 4wd before no problem. Thanks
It is manual shift for the 4wd, and automatic transmission