Delays on the No. 7 subway line nearly ground service to a halt during Monday’s rush hour — the same day the MTA introduced new signals on the line to enhance reliable service.

The transit authority announced on Twitter Monday afternoon that “modern signaling tech,” known as communications-based train control signal system, went live on the entire No. 7 line for the first time.

Less than an hour later, the MTA tweeted 7 trains were running with delays because of a communication problem at the Queensboro Plaza station in Queens.

“The 7 line reached a milestone today with full CBTC activated on every segment of the line,” the MTA said in a statement.

“This afternoon we had a track circuit failure,” it added, saying it couldn’t be sure that the new tech was the problem or not.

The delays — which lasted into the evening commute — caused congestion along the 7 line, enraging straphangers trying to make it to their destinations.

“Where can I submit my Lyft receipt for reimbursement? 30 mins from grand central to queensboro. I’ll be lucky to get home by midnight,” one Twitter user fumed.

“Do you all have a recommendation on how we should get home? Should I just walk from Queensboro or take a bus? How much longer until the 7 is up and running properly?” another straphanger waiting on 7 train service tweeted.

Despite the delays, the MTA said customers will soon reap benefits from the new signals.

“Customers will soon enjoy the enhanced reliability and, eventually, increased train frequencies that CBTC allows, as currently seen on the L line,” it said in a statement.