a braking system for towed vehicles is disclosed which provides for controlled application of hydraulic brakes in a towed vehicle in response to the application of the brakes by the driver of the towing vehicle . an electromagnetic variable valve means provides the responsive braking pressure in a towed vehicle by employing an electric current signal from the towing vehicle to create an electromagnetic force which is balanced against the hydraulic pressure present in the towed vehicle &# 39 ; s brakelines . the variable valve means preferably includes a valve housing 44 , a valve cap 16 , electromagnet means 46 , valve cap switch means 18 for activating a hydraulic pumping means , a hydraulic relief control valve stem means 52 and the pressure monitoring pin means 54 .