the rear window defrost on my 2004 pacifica stopped working, worked fine last winter. When you push the button, the light on the button turns on and you can hear a click like a relay turning on comming from both front doors. The rear heat grid is not damaged and i put a meter the posts on either side and the ground is good, not getting power to the blue w/ white tracer wire on the driver side post. Checked the fuse box, all the fuses are good, doesn't seem like there is one just for the rear defrost, and i couldn't find the location of the relay. Don't know why i hear a clicking in the doors, no reason to have the rear defrost relay inside the front doors.

 

Half of the electronic reasoning doesn't make sense in cars nowadays. Check inside the door panels if that's where you hear clicking... there's got to be something related in there. Unless someone else chimes in with a known problem, you may just have to follow that blue/white wire and see if it's pinched or cut somewhere. If the wiring DOES run through the doors for some reason, oftentimes the spot where the wires run to/from the doors is subject to a lot of movement (door opening and closing) and those wires can wear out and break.