The Ignition Switch's Role
The ignition switch is a multi-position electrical switch located behind the key cylinder (or, on push-to-start cars, integrated into the BCM/start button circuit). It distributes power to critical circuits depending on position: Accessory, On, and Start. When the ignition switch fails internally, it can prevent any of these circuits from receiving power.
Ignition switch failures are not the same as a seized lock cylinder — the lock cylinder is the mechanical barrel you insert the key into. The ignition switch is the electrical component behind it.
Symptoms of a Failing Ignition Switch
- Turning the key produces absolutely no response — no cranking, no dash lights, nothing
- Accessories (radio, blower fan) work in the "accessory" position but the car won't crank
- Intermittent starting — works most of the time but occasionally fails completely when the key is turned to "Start"
- The car stalls while driving for no apparent reason and the ignition seems to cut off
- Dashboard lights and accessories flicker or cut out while driving over bumps
The intermittent nature of ignition switch faults makes them maddening. The car often starts normally at a workshop, only to fail at the worst possible moment.
Ruling Out Other Causes
Before suspecting the ignition switch, rule out:
- Dead battery — no dash lights at all with a flat battery too
- Bad starter relay — click from under the bonnet with dash lights on
- Blown fuse — check the ignition and start fuses
- Faulty neutral safety switch — on automatics, the car won't crank unless the gear selector is in P or N; a bad switch can prevent starting
If electrics are on but the car won't crank, and the starter and relay test fine, the ignition switch's "Start" position circuit is suspect.
How a Mechanic Diagnoses It
A mechanic will use a multimeter to test for voltage at the ignition switch output terminals in each position. No voltage output in the "Start" position with voltage present at the input = faulty switch. This is a relatively quick electrical diagnosis.
Replacement Cost
The ignition switch electrical component (not the lock cylinder) typically costs:
- Parts: $60–$200 NZD
- Labour: $80–$200 NZD (depends on steering column disassembly required)
- Total: $140–$400 NZD
On some vehicles the steering column must be partially dismantled to access the switch. European vehicles are often more labour-intensive. Replacing the lock cylinder (if the key won't turn smoothly) is a separate job and involves a locksmith or dealer for key coding in some cases.
WoF Note
A faulty ignition switch that causes the engine to cut out while driving is a serious safety concern and would be grounds for a WoF fail if detected. An intermittent stall due to an ignition switch fault should be repaired promptly.