What causes tail lights to malfunction?

Hello Paul, there is something I have observed about most cars on the road that I seek your clarification about. I have noticed that 90 per cent of cars on the road have only one of the two tail lights coming on during braking or even nothing at all. What causes these tail lights to malfunction and how can I take care of them to avoid that? Martin

Hello Martin, tail lights and brake lights can fail due to electrical circuitry issues, bulb or bulb housing failure. There are maintenance protocols you can follow to detect or prevent failure of tail and brake lights. For the record, tail lights are the rear lights that come on when you switch your lights on. Brake lights are switched on when you apply brakes while indicators come on when you use the turn signal switch.

All these lights are in the same rear lamp clustre. Tail or brake light failure is usually a result of bulb damage due to age. These lights can also fail due to electrical circuit breakdown caused by blown fuses, corrosion, damaged or loose bulb housings and broken wire harnesses.
A cracked tail light lens can allow moisture to enter the lens and cause short circuits or corrosion which prevent the different bulbs from lighting up. A poorly grounded relay (electromagnetic circuit transfer unit) or a damaged brake switch will prevent the brake lights from lighting up.

You can maintain your tail lights or brake lights to avoid failure. Carry out weekly checks by switching on lights to test tail lights, ask someone to apply the brakes so you can confirm the brake lights work. During servicing all light bulbs should be tested and confirmed. Inspect fuses for corrosion or soot build up and clean them. Also, inspect lenses and check for cracks or damaged seals. Avoid frequent jet washing of tail lights as it wears out seals which allows moisture infiltration.