The Reverse Flow Solenoid has three openings for brake fluid travel. Actuators must be pre-drilled and tapped to accept the return line from the solenoid. All Tie Down Engineering actuators accept a reverse flow solenoid. Verify that your actuator has the return port before buying this style of solenoid. Connecting the reverse flow solenoid is similar to the back flow, however, an additional tube is connected to the return port in the master cylinder. The electrical wire is connected to the reverse lights of the tow vehicle. The reverse flow solenoid has a third port that redirects the fluid to the master cylinder that would be going to the trailer brakes. When the reverse lights on the tow vehicle activate the solenoid, the valve inside the solenoid redirects the brake fluid to return to the master cylinder. An advantage to the reverse flow is that the issue with backing up an incline is not an issue as you see with a stop flow-style solenoid. Should the reverse flow solenoid become clogged or malfunction, usually the worst is that no pressure goes to the trailer brakes, where if a stop flow solenoid malfunctions or becomes clogged, it can hold pressure in the brakes causing them to drag.