Q: Headlights brighten and then dim while driving over bumps

asked by on November 09, 2015

When I drive over a bump, my headlights get brighter and then dimmer. Why does this happen?

Often headlights seem to get brighter or dimmer when there is a bad connection or a failing switch. Since a bad connection can be inside the light bulb itself, I always start by inspecting the bulbs first to see if the filament is broken. This often happens when the car goes over a particularly violent bump. A mechanic can replace the broken bulb with a new one. If the problem persists, the next step would be to have a mechanic perform an electrical system inspection, where the technician will look for a loose connection at the headlight plug connector, a loose or corroded ground connection or a failing headlight switch.

Some newer cars use high-intensity discharge (HID) bulbs that require a ballast to regulate the voltage going to the bulbs. A faulty ballast won’t provide enough voltage to your headlights, so this can also cause the headlights to flicker.

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