Motorists in Perth’s northern suburbs pulled over by what they thought was an undercover policeman overnight will not be the ones to front court for breaking the law.

Instead, an 18-year-old male driver who allegedly pretended to be a police officer by mounting a red and blue emergency light to his car before pulling unsuspecting motorists over will face court.

The white Nissan ute and emergency light was seized by police. Credit:WA Police

Police allege the man was driving his white Nissan Navara utility erratically in the Ocean Reef and Heathridge area on Saturday night through to the early hours of Sunday morning with the dash-mounted light on.

A police spokeswoman said they received calls from the public about 11pm on Saturday about the Nissan Navara being driven erratically and the occupants using the light to pull other cars over.