Filament Testing

To locate breaks in grid wire filaments, attach a voltmeter to middle portion of each filament. Attach other meter probe to vertical section of window grid.
If a grid is broken, meter will register zero volts or battery voltage, depending on if grid is broken between or outside test leads. If wire is unbroken, meter will register about one half of battery voltage. To locate break, move probe along wire until the meter needle moves abruptly.

Fig 1: Voltage Test For Broken Grid Filaments