The one you received is and aftermarket piece that fits more than one application. I believe it also fits A-bodies. I believe I purchased the same one for my 73 Challenger from Advance Auto. Did the switch come with any loose female connectors? You can cut off the male connectors(and extra length of wire) and crimp on the correct ends.

Also, my original switch didn't use and extra ground wire. There was an empty slot in the connector. The new switch has a thinner gauge black ground wire in the connector where my original one was blank. Check to make sure you don't have a "hot" wire on the other side of the plug. On my 73, there were two orange "hot" wires on the dash harness side of the plug where that extra ground wire was located. I just removed the ground wire from the connector and tied it out of the way. It's not needed. I believe the instructions indicated that the extra ground wire was used on the A-body applications.