pabubby, finally replaced my cab light. I made it harder job than it needed to be. If yours are like mine, after you remove the caulking, just twist the light out of the aluminum bracket that you can see in the attached photo. Hopefully these pictures will help you. At least next time I'll know what to do.
If you have the same light I have look at the back of it as well and it will give you a good idea on how to twist the light and remove it. I didn't need the string for the power plug but I just verily had enough wire to pull it out to plug the new light in. Job done though!
Here is a link showing the Truck-Lite mounting bracket for my light.
Further update, I just checked the continuity of my old light and it appears ok. Double check to make sure your did not just come unplugged as I think this it what actually may of happened to mine.