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A vehicle's indicators flash rapidly on the nearside only, and all four bulbs on that side appear to illuminate.

Which cause is most likely?

  • A.A poor earth reducing the current through the circuit
  • B.A failed bulb, which cannot be the cause because every lamp on that side has been observed to illuminate
  • C.A faulty flasher unit
  • D.A blown fuse, which would prevent the lamps from operating at all rather than causing them to flash rapidly

Answer: A

A high resistance earth reduces the current the flasher senses, so it doubles its rate even though the lamps still glow. The lamps are usually noticeably dimmer as well, which confirms the diagnosis. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision. The shared behaviour explains why these belong together and the differences explain why both exist. Checking which component actually carries the load settles most questions of this kind at once.

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