Connect the power source Positive lead to NO, and the C leg to the Positive lead going to your light.
Connect the power source Negative direct to the Negative lead going to your light.
Do not connect anything to NC.
NO will be hot (have power all the time), C will be hot when the relay is commanded on.
NC will never be hot.
C = Common connection
NC = Normally Closed connection
NO = Normally Open Connection
C will be used as the supply for NC or NO depending on your situation. If you want to switch negative for example, you will connect C to ground and use NC to "receive" that ground when the relay is switched off and use NO to "receive" ground when the relay is switched on.
This is known to us Auto elecs as a simply "Change Over" relay. It means simply that NC and NO are never common to each other. They are only common to C and only seperately and never simultaneously.
I would wire it up with your LOAD, item you are supply the + or -, to the NO side of the relay so that the relay is only drawing current when you want to turn the item on.
**This is a strange way of labelling a relay. I would try and make things easier for yourself by thinking of NC as AT REST or WHEN RELAY IS SWITCHED OFF and NO as RELAY SWITCHED ON.
Hope it helps!
****Just realised this thread is over a year old! FAAAAAAAAAAAHHH-