The plastic cover pieces can be extremely brittle. Some slotted clips similar to door panels hold on the plastic pieces. There is nothing under there except a wire connecting to the metal bar by a female spade connector. The metal bar on the other side is screwed to the metal window pillar for a ground. When energized there should be voltage (~12V) on one metal bar and near 0V on the grounded side. If no voltage, I would suspect the switch or a fuse. If the voltage is there but no defrosting there may be a break in the window circuit. There are repair kits it you can find the break. If the contact at the window is corroded, try some electrical contact cleaner. It the contact is lifting off the window it may be possible to glue it down again.