I have a 1999 Land Rover Discovery 1, SD model. How come my 4-wheel drive light on the insterment cluster (dash board) isn't working. It wont come on no matter if I'm in high or low on the Diff-loc side or the right, normal driving side. I know the 4-wheel drive is working, the front end is getting power. Is it that the light is burned out, or is there a switch thats not working in conjunction with the transfercase lever?