Your vacuum wipers. The line from the inlet manifold goes to the bottom of the petrol pump, the pump is petrol pump on the top and a vacuum pump on the bottom. Then out to the wipers. When in good nick, this system work very well. If it dont work well or the wipers stop or nearly stop when you floor it on the road, something is not working. There'd be a leak somewhere, in the pipe fittings or such like. Often the pipe that goes from the vacuum pump to the wipers is perished where it buggers off into the bulkhead and off to the wipers.