Updated at 12:42 p.m.:
Power was restored Saturday morning following an overnight outage affecting 1,521 customers in Diamond Bar and Industry, SCE officials said.
Wires were cut at a circuit breaker utility box at 525 Grand Ave., according to Southern California Edison's Maureen Brown; the power went out at 9:50 p.m., Brown told Patch.
The boundaries of the area where customers lost power were Lemon Avenue, in Industry, to the west; Lycoming Street, in Walnut, to the south; Sun Street to the north and Gentle Springs Lane, in Diamond Bar, to the east.
Repairs were completed and power restored at 8:30 a.m., Brown told Patch.
The theft of copper wire from a utility box caused an outage that knocked out power overnight to some 1,600 customers in Diamond Bar, Los Angeles County sheriff's officials told Patch.
According to LASD Sgt. Angie Wilkinson, the theft occurred in the area of the vacant Diamond Bar Honda lot near the Pomona (60) Freeway.
Wilkinson said there is a utility box outside the closed dealership.
"They opened it up and cut the wires," Wilkinson told Patch.
There was no suspect information available.
Power was set to be restored by noon Saturday, the sergeant told Patch.