Check Filament

When measuring voltage, wrap tin foil around the top of the negative probe. Then press the foil against the wire with your finger.

Fig 1: Pressing Test Probe To Filament Grid
Courtesy of NISSAN MOTOR CO., U.S.A.
Attach probe circuit tester (in Volt range) to middle portion of each filament.

Fig 2: Attaching Probe Circuit Tester (In Volt Range) To Middle Portion Of Filament
Courtesy of NISSAN MOTOR CO., U.S.A.
If a filament is burned out, circuit tester registers 0 or battery voltage.
To locate burned out point, move probe to left and right along filament. Test needle will swing abruptly when probe passes the point.

Fig 3: Identifying Burned Out Point
Courtesy of NISSAN MOTOR CO., U.S.A.