The voicecoil wires on a Grado enter from the outside.
It can be seen (well, it cant) in this photo under the little heart shaped dab of something white:
If this were an SR-(whatever) you would be looking down the tube and that little dab of white stuff would be up against the wall of the tube.
I would test EVERY connection systematically: Both channels at the plug as well as at the drivers. Some multimeters will not work if there is a layer of flux over the solder joint.
If you had torn the solder pads off you would know. BUT if excessive heat is applied it is possible for the voice coil wires to basically burn up, as mentioned.
I would get a solder sucker, and clean everything up. After that remeasure. If you still cant find continuity chalk it up to experience and use the cups to make a headphone stand in the fashion of headphile. Use the functional driver to experiment with DIY dynamic microphones, and use the busted driver as a reminder to practice on cheaper stuff.
Plan B is to call Grado and explain your predicament to them. In the past they have been quite helpful to DIY'ers whose projects have gone awry, although they cant be expected to warrant this kind of problem and do take a bit of your money for it (not much really).