If I understand your question, the wire to the carburettor needs to become live when the ignition is switched on...this allows petrol to flow into the carburettor, allowing the engine to run. As for the other wire, it sounds like it is the engine shut off wire....when it is connected to ground, the ignition coil stops producing a spark, and the engine stops. Try running the engine with this wire disconnected.
John, July 2009
