A mate of mine with a 90 TD5 has recently taken his pride and joy to a garage and they informed him it needs a new transfer box !!! I took it out for a drive today and the box is fine in high and low ratio but the TC light is now on 
I know nothing about TC or possible faults or what to look for...
Any help would be appreciated thanks

I know nothing about TC or possible faults or what to look for...
Any help would be appreciated thanks