[Kevin Sevcik]

What you probably want is a Select block. You'll find it in the Programming>Comparison palette. It takes a boolean input and uses it to decide which of two other inputs it should output. So you'd use it in combination with the relay enum constants described by airnate to control the relay. You'd wire an "Off" constant to one input, a "Forward" constant to the other input, and then have the boolean input pick which one is actually sent to the relay set vi.