The ones on the top of the cab.
Were ever a legal reqiurement?
Recall they seemed to appear in the 70s with the influx foreign motors . . . apart fom the F86 
They are a requirement for all vehicles first used after 1st April 1991, where the vehicle is greater than 2.1m in width.
Trailers first used after 1 October 1990 also require them to be fitted, same width rules apply.
This from the 2012 edition of the HGV Inspection Manual published by the DfT.
what about fuel tankers that three amber marker lights above the windscreen. is that anything to do with adr regs?
dilbert:
what about fuel tankers that three amber marker lights above the windscreen. is that anything to do with adr regs?
Thought that was Hinos,3 lit … . speeding?