The Ignition input on Siren Marine units are looking for positive voltage. Connect it to your ignition or some other positive source that is only on when the engine is on.
Engine Hours is looking for ground. To monitor an engine or generator using this input, connect the coil side of a Siren Marine DC Relay to a positive source that is only on when the engine is on. Then connect the normally closed (NC) switch on the relay between the Engine Hours input and ground.