How Surge Brakes Work:

Surge Brakes are engaged on your boat trailer when the brake actuator is pushed forward on the hitch by the tow vehicle stopping.  Compression of the actuator allows the master cylinder to release hydraulic fluid.  Therefore the build up of hydraulic fluid forces the brakes to begin working.

Backing up your Boat Trailer:

An automatic brake lockout is recommended if the trailer has disc brakes.  A 5 wire-wiring harness is equipped with a wire that connects to the towing vehicle back up lights.  A 12 volt electrical signal from the tow vehicle back up light circuit energizes the pressure control unit.  Hydraulic pressure is then prevented from building up so the brakes will not come on allowing the boat trailer to back up.

Drum brakes will usually back up without complications.  A lock out key can be used if necessary.