Question

A vehicle came in with a left tail light out.

Replacement of the bulb did not fix the problem
An incandescent test light illuminates when probing the power side of the bulb socketNow the test light clamp is hooked to a powerThe test light illuminates when probing the ground side of the socket as well

Technician A says the ground circuit is probably good
Technician B says there may be a fault in the physical connection between the bulb and socket

Who is correct?

Answer 1

Technician B is correct that there may be a fault in the physical connection between the bulb and socket. A functioning ground circuit should not cause the test light to illuminate when probed, suggesting an issue with the ground or connection.

Step-by-step explanation:

When addressing a vehicle's electrical issue, where a left tail light is not working despite the bulb replacement, a careful diagnosis is needed. Technician A is incorrect to suggest the ground circuit is probably good just because using a test light with the clamp hooked to a power source causes it to illuminate when probing the ground side. This could indicate a problem with the ground since the test light should only illuminate on one side, typically the power side, if the ground were good.

Technician B, who suggests there may be a fault in the physical connection between the bulb and socket, is correct. This could be due to corrosion, a damaged socket, or a misalignment preventing a good electrical connection. Since the test light illuminates on both sides, it means we have a power feed at the socket, but not an adequate ground return, leading to the bulb not lighting up.