The rear window defroster only clears a spot about the size of a silver dollar after about 15 minutes of use. I have checked and there is voltage to the grid. As I check the voltage across the grid, I have full voltage up to the ground terminal. I checked the voltage at the ground terminal and there is a drop in voltage of 2-3 volts. I checked the ground wire with an ohm meter and it is fine. If I check the resistence between the ground terminal on the defroster and the grid, I get a reading of about 120 with the meter on the 10k scale. I am assuming the is a problem with the ground tab's connection with the grid. Is there a way to fix this without replacing the window or the whole defroster grid?