Braking system for towed vehicles

A braking system for automatically braking a towed vehicle having an engine, a battery and a braking arrangement including a brake pedal, the towed vehicle being detachably coupled to a towing vehicle also having an engine, battery and braking system and having a vacuum line using compressible fluid and a braking unit including an electrical control circuit comprising, in combination, vacuum responsive actuator means on said towed vehicle, means for operatively connecting said actuator means to said towed vehicle brake pedal, a source of vacuum on said towed vehicle, conduit means including a normally closed, solenoid operated valve for communicating said source of vacuum with said actuator means, circuit means on said towed vehicle including a normally open breakaway switch for connecting said towed vehicle battery to said solenoid operated valve, means for detachably connecting said circuit means and said conduit means to said control circuit and said vacuum line and said towing vehicle respectively in the coupled condition of said towed and towing vehicles for energizing said solenoid operated valve and supplying a vacuum to said actuator means to brake said towed vehicle during the braking of said towing vehicle, said breakaway switch being responsive to the uncoupling of said towed and towing vehicles for energizing said solenoid operated valve to apply a vacuum to said actuator means from said vacuum source for braking said towed vehicle should the towed vehicle be dissociated from the towing vehicle while being towed.