Why, oh, why does it take five months to fix the Red Line signal system?

Please don’t tell me the MBTA blacksmiths are forging parts one by one.

Officials are telling riders it will take until October for service to return to normal after a June 11 derailment near JFK/UMass Station in Dorchester damaged the signal system.

To find out why signal repair might be so labor intensive, I went where few Red Line riders have gone: the T’s signal sheds.

Three of them were mangled when the train derailed on the track’s right of way. Rebuilding those sheds was the easy part (all done), but salvaging the equipment inside has been more difficult.

For starters, when you’re still using a signal system from the 1970s, it can be hard to find parts. In this case, the manufacturer stopped making them five years ago.

Exacerbating the situation is that so much of the equipment on the MBTA is custom made. Officials can’t even use spare signal parts from another subway route — like the Blue or Orange Line — because they aren’t compatible.

Joe McNall, the MBTA’s director of signals and communications, likens the repair effort to hunting for parts for a Ford Edsel.

“They don’t make them anymore,’’ said McNall, standing in one of the new sheds that — unlike the previous ones — have been built far from the tracks, in an MBTA employee parking lot by JFK/UMass Station. If a train hits them there, we’ve really got problems.

The signal equipment looks very old-school: a series of green circuit boards surrounded by lots of wires and cables. Think of a decades-old science project gone bananas.

The circuit boards create, send, and receive electronic signals that travel along the rails. These signals help manage the flow of trains by detecting where they are, enforcing travel speeds, and maintaining safe distances between each one.

Signals also allow trains to communicate with a control center to provide real-time train location data and the route that each train will take.

With part of the signal system down, the MBTA has had to rely on manual and visual signals, as well as dispatchers. That’s why Red Line service has been slow. T officials are still advising riders to factor in an extra 20 minutes to their commutes, though there has been incremental improvement as more signals get fixed.

Typically, signal repairs are done in an MBTA facility in South Boston, but the damaged circuit boards were sent back to the French manufacturer, Alstom, for repairs at its Rochester, N.Y., facility.

After the repairs, the circuit boards need to be tested, and that can take a while. Just fixing the signal system between the Broadway and JFK/UMass stations took a month. Testing the equipment took another 2½ weeks. Most of the testing had to be done during off hours.

“It’s a tedious job,’’ McNall said. Most of the damaged circuit boards have been repaired, but integrating them into the system of hundreds of boards and thousands of wires will take more time. The new timeline has service returning to normal on the JFK/UMass-to-Fields Corner stretch in early fall, and closer to October for JFK/UMass to North Quincy.

“Every single day we are pushing to collapse that schedule as much as we can,’’ said Erik Stoothoff, the MBTA’s chief engineer.

So what lessons are to be learned from the derailment debacle?

“We need to stop deferring the maintenance. We need to repair and replace,’’ Stoothoff said.

That is the object lesson here. Never again should we run MBTA equipment into the ground so far past its life cycle that when it comes time for repairs, the manufacturer has stopped producing the parts.

Compounding our commuting misery is the ungodly length of time it takes to repair and replace anything at the MBTA. The T is trying to make up for lost time with a plan to close stations on some weekends in the fall along stretches of the Red, Orange, and Green lines to accelerate repairs.

Consider how long it has taken to replace the aging signal system: In 2015, the Baker administration identified that it needed upgrading. In 2018, the MBTA awarded a $218 million contract for a computerized signal system. It won’t be delivered until 2021 for the Red Line and 2022 for the Orange Line — coinciding with the arrival of new cars, which also seem to have taken forever to deliver. (The first six Orange Line cars are expected to be put into operation starting Wednesday.) The new signals, combined with the new cars, are expected to reduce signal failures and delays, and allow for more frequent service.

The governor is trying to cut the red tape in the procurement process through a recently filed $18 billion transportation bond bill. The Pioneer Institute, a conservative think tank, in a report last week, also doubled down on the notion that the MBTA needs to speed up its procurement process and improve delivery of capital projects. Two big takeaways from that study: Relax subcontracting restrictions and hire experienced project managers.

“The real tragedy is that they are having to replace an old system which is going to be replaced with a modern sophisticated digital system in the next two years anyway,’’ said Ian Ollis, a visiting senior researcher who authored the report with Greg Sullivan, Pioneer’s research director and former state inspector general.

Pioneer also warned that other transit systems have faced major delays and cost overruns when trying to implement new signal systems. “These contracts, if they are not done properly, can be delayed for years,’’ Ollis said.

Just like T passengers have been. Let’s not go through this again.

2015

The Baker administration identified that it needed to upgrade the signal system.

2018

The MBTA awarded a $218 million contract for a computerized system.

2021-22

The Red Line and the Orange Line will get the new signal system — coinciding with the arrival of new cars, which also seem to have taken forever to deliver.

Shirley Leung is a Globe columnist. She can be reached at shirley.leung@globe.com. Follow her on Twitter @leung.