TOKYO (March 15, 12:30 p.m. ET) -- Japan’s Fair Trade Commission is investigating four Japanese headlamp makers for evidence of possible price fixing, the companies said today.

The investigation widens a series of antitrust probes that until now were mainly focused on wiring harnesses but also, in Japan at least, included windshield wipers, radiators, engine starters, alternators and bearings.

Koito Manufacturing Co., Stanley Electric Co., Mitsuba Corp. and Ichikoh Industries Ltd. said they’re being investigated by Japan’s antitrust watchdog for price fixing.

Japan’s Fair Trade Commission is investigating auto parts makers for unfair trade practices, said spokesman Isao Kasubuchi, without specifying how many or which companies. Kyodo News and the Nikkei newspaper first reported the probe.

Koito and Stanley will cooperate with the agency’s probe, the companies said in separate statements to the Tokyo Stock Exchange. A Mitsuba spokeswoman and an Ichikoh spokesman also confirmed the investigation when reached by telephone by Bloomberg.

The Nikkei said the Fair Trade Commission carried out raids at 20 locations, including the headquarters of Koito and Stanley Electric in Tokyo, Ichikoh in Isehara City, Kanagawa Prefecture, and Mitsuba in Kiryu City, Gumma Prefecture.

It also said the four companies hold a 90 percent share of Japan’s headlamp market, which it estimated at 200 billion to 300 billion yen ($2.43 billion to $3.65 billion) in annual sales.