Why cars fail their MOT on lights and electrics (and what it costs)

Lamps and electrical faults are the single most common MOT failure at 10.36 percent of cars. What fails, why, and what it costs to fix on a salvage repair.

MOT DATA · 4 min read

The most common failure of all

Lamps, reflectors and electrical equipment are the number one reason cars fail their MOT, showing up on 10.36 percent of all tests. The good news for anyone buying cheap is that most of these faults are trivial: a blown bulb, a cracked lens, a misaligned headlight or a dead number plate light.

Why it fails so often

Bulbs are consumables and fail constantly, and a single dead bulb is an instant fail. Modern cars add complexity with LED units and self-levelling headlights, which are more expensive when they go, but the bulk of failures are still simple bulbs and lenses the previous owner never bothered to replace before the test.

What it costs to put right

At the cheap end this is a few pounds and ten minutes. A standard bulb is a couple of pounds, a plate lamp not much more. It climbs if you hit a full LED headlight unit, which can run into the hundreds, or a wiring fault that needs tracing. For a salvage repair, budget almost nothing for basic bulbs and check separately whether any headlight units were damaged in the incident.

The salvage angle

A car that fails its MOT only on lights is one of the best cheap buys there is, because the fix is close to free and the failure scares off other buyers. But if the car is a front-end accident salvage, headlight units are a common casualty and a genuine cost, so separate a cheap bulb from an expensive smashed projector unit before you bid. The Analyzer factors headlight replacement into the repair estimate when the damage photos show it.