an Audi80 SE500 draining all the battery current when engaged in reverse gear.

It totally drains the battery when you place it in reverse? Is the battery actually dead if you try to restart it after this? Have you checked for shorts in the wiring?

yeah i realised short circuit in the reverse wiring and rectified it,but the problem is i also -discovered the vehicle was started without water in the radiator. So when i started it,after prolonged cranking, i poured water into the evidently thirsty radiator,but it was occasionaly back spitting it,worse still when you give it more revs. But is that not typical of a warped engine head?

Yes, that can indicate a bad head gasket.