Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsLighting Systems Diagnosis and RepairMedium
A vehicle's right front turn signal and right rear turn signal are not illuminating, but the left side turn signals operate correctly. The dashboard indicator for the right turn signal also does not illuminate. Fuses for the turn signal system are checked and found to be good. Which of the following is the MOST likely cause?
- AA faulty flasher relay for the right side.
- BAn open circuit in the ground wire for the right side turn signals.
- CA defective multi-function switch (turn signal switch).
- DBurnt out bulbs in both the right front and right rear turn signals.
Show answer & explanationAnswer & explanation
Correct answer: C. A defective multi-function switch (turn signal switch).
Since both the right front and right rear turn signals, as well as the dashboard indicator, are not working for the right side only, and the fuses are good, the most likely common point of failure is the multi-function switch which directs power to the right turn signal circuit.
Why the other options are wrong
- A. Most vehicles use a single flasher relay for both left and right turn signals. If the flasher relay were faulty, both sides would be affected or neither would flash.
- B. An open ground would prevent illumination, but it's less likely to affect both front and rear bulbs and the dash indicator simultaneously unless they share a common ground point that has failed, which is less common than a switch failure.
- D. It is unlikely for both the front and rear bulbs on one side to burn out at the exact same time, and this would also typically cause hyper-flashing on the dash indicator (if it were still working) rather than no illumination.
Multi-function Switch Fault
A fault in the multi-function switch (turn signal switch) can prevent power from reaching specific lighting circuits, leading to a complete failure of lights on one side or particular functions.
- Controls turn signals, sometimes wipers, high beams, and cruise control.
- Internal contacts can wear or corrode, preventing current flow.
- Failure affects functions routed through that specific part of the switch.
Memory trick: One side out? Switch it about!