Common problems with a rear defroster include a loose wire indicating a faulty solder connection, a break in the gridwork associated with a visible scratch in the paint, and lack of power due to a blown fuse or worn wiring. Another potential reason for rear defroster problems is a break in the painted circuit.
To check for chips or scratches in the painted circuit, examine the connection tabs beside the painted grid, and check for a loose wire that needs firm attachment to the grid. Try reconnecting the wire if it has a connector on its edge. Otherwise, reattach the wire by using a kit containing soldering paste, which is a type of glue with metal contents for effective conduction of electricity.
Check the grid lines for any break. If there are no scratches or missing areas in the paint, use a test light designed for rear defrosters. Determine if the defroster grid receives any power by using the defroster test lamp. The process requires detaching the wires from both sides of the defroster grid and touching the edge of the tester to the wires.
An illuminating lamp indicates the presence of power, while an unlit lamp means you need to examine your fuse and replace any defective fuse. Find out if the defroster grid receives power by disconnecting the wire near your vehicle's passenger side, linking the test clip to the wire and touching the other lamp wire to the circuit's other tab without disconnecting the wire.