A piece of underground PG&E equipment failed early Tuesday in a core Santa Rosa area, knocking out power to a huge group of customers along the northern Mendocino Avenue corridor.

At 6:55 a.m. the top of a splice box came off in the area of Mendocino Avenue near Steele Lane, PG&E spokeswoman Jana Morris said.

That malfunction caused power and traffic lights in the area to cut out, affecting 4,389 business and residential customers.

Power was restored to all but 26 customers by 8:15 a.m., Morris said.

By mid-morning, with traffic lights at Mendocino and Chanate Road still not functioning, Santa Rosa police asked for portable stop signs to help with traffic, said Sgt. Lisa Banayat.

Morris said power was restored to all customers by 10:30 a.m.