The Combine does not turn on until there is a fully grown wheat plant inside its area. Then it will activate by clearing the wheat, and store it in a chest next to the combine, or if connected to pipes will send the wheat along the pipes to whatever destination they connect to.
3. Iron Electron Tube
1. Sturdy Casing
1. Basic Circuit Board
This video demonstrates how to use all forestry farms, including the combine.
Below Is a Video showing how to make an automatic wheat farm in conjunction with a Farm