NAHANT – National Grid worked to restore power to 1,800 customers who lost electrical service in Nahant and Lynn Thursday night.Of the 1,800 customers, most were from Nahant and 500 were from Lynn. Service was lost at about 8 p.m. Thursday due to an underground cable failure in Lynn in the vicinity of the Lynnway, Amy Atwood, spokesperson for National Grid said Thursday night.Atwood said power should be restored to the affected customers sometime between 12:30 a.m. and 1:30 a.m. Friday and “that’s an estimate.””We’re trying to get our customers back on before we figure out a cause of the outage,” Atwood said.The street lamps on the Causeway were among some of the lights that went dark.The Nahant Police Department was flooded with calls Thursday night. Officers kept in close contact with National Grid crews as the problem was being fixed.