Burtonsnow157

I have a 2003 GT with 98k miles. The rear window does have tinting. The defroster worked since the tinting was put on so the tint more than likely is not the culprit here. As far as i can tell neither the fuse or switch/timer are bad which is supported by information below.

I just bought a multimeter and these are my findings.

Car running defroster switch pressed on (light on)

Drivers side - grid, tab and, harness all get around 14 volts - seems good.

Passenger side - with the harness on that side removed, the tab gets 14 volts, and so does the grid, the harness by itself does not get any voltage and once you reconnect the harness, the grid and the tab go dead to 0 volts (which clearly seems what is causing the problem) i have cleaned the tab and the harness and i will do so again, but does anyone have any other suggestions?

edwin108

With both tabs connected, I would expect that one tab has battery voltage while the other has ground (0 volts). You can check the grid for continuity along the lines:

Doctor Defroster

If I understand the problem, with both the ground and power wires removed from the defroster, you measure 12-14 volts on the defroster connectors. However, if you reconnect the grounding cable to the ground tab on the defroster, the voltage that was on the power tab disappears.

This indicates a high resistance somewhere between the battery and the power tab. The most likely place is the defroster relay. Every time the defroster is turned OFF, there is a small spark on the relay contact, causing tiny bit of corrosion on the silver contact surface. This causes a poor connection, which burns through, and you never notice it because a good contact is made very quickly. Eventually, however, the oxidation accumulates to the point where the resistance gets high enough that the current doesn’t create enough heat to break through. Your meter uses very little current (~1.4 microamperes), which is easily supplied by the poor connection at the contact, but nowhere near enough to supply the ~10 amperes required by the defroster.

While the relay is the most likely culprit, any slightly loose connection from the circuit breaker or fuse to the defroster is suspect.

If the resistance were very high in the defroster grid , or the grid was “open”, the voltage at the tabs would be unchanged if there were no failure in the source. The only failure in the grid that would cause the voltage at the tabs to zero volts is a dead short, which would clear the fuse immediately. Since that is not your problem, the grid is likely to be fine. Normal resistance for a grid runs between about 0.8 ohms and 1.5 ohms. You can check it with your ohmeter.

If the tabs come off the defroster then use the Frost Fighter Tab Bonding kit, if the gird is broken the the Frost Fighter Grid Repair Kit. www.frostfighter.com