A fail-safe signal injection system includes a fail-safe system controller that receives a control command and initiates to bypass a first system to inject a control signal into a second system responsive to the control command. The fail-safe signal injection system also includes a signal injection circuit implemented to inject the control signal into the second system responsive to power applied to the signal injection circuit, the signal injection circuit further implemented to fail-safe without the power applied, and thus operates to pass a control input from the first system through to the second system.