There are two inputs on the MTC for monitoring engines or generators. On the MTCs terminal connector board, the inputs are Ignition (Engine 1 in the app) and Engine Hours (Engine 2 in the app).
The Ignition input is 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.