encryptor:
Also, the backend of the relay would be connected to the arduino Vcc, GND, and digital output pin.
NO !!!! NO NO NO !!!!
you need to put 12VDC on the back end for power. straight 12VDC. un-switched.
then the Arduino puts out a signal to power the opto. it shares a ground reference with the 12VDC.
if you try to connect the Arduino Vcc to the 12 volt coil, bad things will happen.
double check the data sheet on that relay to make sure.