TOKYO — Japanese investigators have identified the causes of fuel leaks and other problems with Boeing’s 787.

An oil leak was caused by an improper paint job that led to a switch not working properly, while inadequate taping led to cracks in cockpit glass, and a faulty part led to braking problems, according to the Transport Ministry’s investigation released Friday into problems that occurred with the 787 Dreamliner in January.

The government issued orders to fix the problems with 787s operated by Japan Airlines and All Nippon Airways, the country’s two major carriers and the biggest customers for Boeing Co.’s new jet.

All 50 of the 787 jets in service around the world have been grounded for more than a month after a lithium-ion battery in a 787 operated by ANA overheated Jan. 16, forcing an emergency landing in western Japan. Earlier in January, a lithium-ion battery caught fire in a Japan Airlines 787 parked in Boston.

Boeing and U.S. authorities are also investigating, but Friday’s findings shed little light on the main problem.

Separately, the Japanese ministry said this week it had found the ANA jet’s auxiliary power unit had been erroneously wired to the main battery that overheated.

ANA, which has 17 Dreamliners in its fleet, and JAL, with seven, have had to cancel hundreds of flights over the 787 woes.

JAL and ANA have released plans for flights without the 787 through the end of March, but have not said what they plan to do in the long term. Both companies have said they are ready to seek compensation from Boeing.