OPERATION No DV. 390-0 : Checking the hydraulic components on the vehicle 12. Checking a brake pressure switch. a) By means of plugs stop the openings of the feed pipes for front suspension «a» and rear suspension «b». Connect the brake control valve feed pipe to end piece «c» of the three-way union. Tighten the pressure regulator bleed screw. Start the engine to obtain the cut-in pressure then switch off.