Possibly mistaken dealer tech?
There's nothing in the power line to the rear gate (hatch) window defogger.
Where is that plastic-covered module? Is it in the rear gate, above the window? If it is, then it's the radio antenna amplifier.
The radio antenna amplifier has wires coming in (signal, power) from the body, and wires going out to the grid on the glass, so it could look as if it's connected to the defogger grid, but isn't. (There's two separate set of grid wires on the rear window -- the radio antenna, and the defogger.)
There's nothing in the power line to the rear gate (hatch) window defogger.
Where is that plastic-covered module? Is it in the rear gate, above the window? If it is, then it's the radio antenna amplifier.
The radio antenna amplifier has wires coming in (signal, power) from the body, and wires going out to the grid on the glass, so it could look as if it's connected to the defogger grid, but isn't. (There's two separate set of grid wires on the rear window -- the radio antenna, and the defogger.)
