Primary coil questions

Hello,

The primary coil on my bike went bad, so I bought a NOS one off of ebay. My original coil had two wires a black and green. The new coil has three a black, green and red. what is the red wire for? I installed the coil and connected just the black wire to the coil and there was no spark. There is no power comming out of the black wire, but there is voltage at the green wire. I don't get it does the red wire need to be grounded?

Thanks, Sean

Can the ebay seller help?