Blinking 4wheel drive on dash panel

Describe your problem. Just engaged 4 wheel drive on my 2000 Toyota 4 runner and the dash panel light will not stop blinking. In the past when I have used 4 wheel and it is engaged the light blinks for a short time and then stops, remaining fully lit until it is disengaged. 4 wheel works (meaning it turns on and off)but the light continuously flashes. It is it a sensor or fuse or? And approximately how much would it cost to fix? If I didn't fix would it cause more problems?