Broken rear defogger

The rear window defogger on my wife’s 2007 Chevy Impala does not work. I can get a reading(ohmns)through the Window but no current through the wires when the switch is on. I could not find a fuse so I changed the relay and it still does not work. When I push the switch the light comes on but nothing happens. I did threaten to hit it with a hammer but still no good. It’s cold and snowing here in Pennsylvania and my wife wants it fixed. Please can you help. Thanks, Nigel the great.

The usual problem is damaged metal tape. Your description does not exactly fit, but that is still where I would start.

How exactly did you measure the ohms? Can you get the the connections where the wire attaches to the window? Did you measure ohms there? How many ohms did it register?

Do you get 12V at one of the connections? Do you have ground continuity on the other connection? The biggest problem is when the soldered lugs to connect the wires to the grid on the windows separate, cutting the circuit. The other is a broken wire.

Cleaning the back window can remove (open) one of the conductive traces on the glass, breaking the circuit…How is the ground configured? A wire or are the traces grounded directly to the car body? All hidden by the trim no doubt…They sell trace repair…It’s like conductive nail polish you brush on to restore current flow…

With the switch on I do not have any voltage where the wires connect to the back window. I hava an Ohmn meter and do have a circuit through the back window.

The rear defroster relay is controlled by the HVAC control module relay driver. Remove the rear defroster relay and jumper a test light between the coil side of the relay socket. Now turn on the rear defroster. If the light doesn’t illuminate the relay driver in the HVAC control module isn’t working.