According to useful information found on this news group, I was able to diagnose the ABS fault with my 1991 RR classic 3.9. The flashing pattern of lights revealed that it was something to do with the stop light switch. I've replaced the switch, the brake pedal spring and checked the wiring: It's all OK, yet when the ABS warning light is still on and the diagnostic still shows the same fault.
When I bought the new parts the guy at the garage said that I might fine it difficult to reset the ABS unit, which seems to be the case: -Can anyone advise me how this can be done? Or alternatively what else might be wqrong with it?