Red Flashing Light Problem

I have a VW Golf GTI 1985 B Reg,
In the centre of the temperature gauge there is a red flashing light when the engine is running.
The water flow, oil and water temperatures are ok, and the radiator fan cuts in when required.
A search of the electrical diagrams in the Haines Manual has proved fruitless.
Can anyone tell me what that flashing red light is for and does it indicate a problem.

Thanks in anticipation.