The Max is Boeing’s most important plane, with about 5,000 ordered by airlines around the world. But as the grounding has dragged on, Boeing said it would temporarily shut down its 737 factory, jolting thousands of suppliers and stoking the concern of President Trump.

Boeing abruptly fired its chief executive late last month after he alienated the F.A.A. and airline customers. His successor is now contending with the fallout, as Boeing’s share price has fallen by 21 percent and the company faces tens of billions of dollars in charges related to the grounding.

Regulators have suggested that the Max could be approved to fly again by the spring, a timetable that could still hold. The company says that even if it needs to fix the wiring issue, it would only take one to two hours per plane to separate the wiring bundles on the Max using a clamp.

“We are working closely with the F.A.A. and other regulators on a robust and thorough certification process to ensure a safe and compliant design,” Gordon Johndroe, a Boeing spokesman, said in a statement. “We identified these issues as part of that rigorous process, and we are working with the F.A.A. to perform the appropriate analysis. It would be premature to speculate as to whether this analysis will lead to any design changes.”

Investigations by international regulators into the cause of the two Max crashes determined that pilots of those flights did not respond as quickly or effectively as Boeing and the F.A.A., using accepted industry standards, presumed they would when designing and evaluating the MCAS software.

So in developing a software update for the Max, Boeing and the F.A.A. recognized that the previous industry assumptions should be changed, and that they needed to consider what would happen if it took crews much longer to act in the face of emergencies.

Using that new set of assumptions about pilot reactions, Boeing discovered that if two wire bundles placed close together toward the rear of the plane caused an electrical short, it could lead to a catastrophic accident. The wiring connects to the motor that controls the stabilizer, the horizontal fin on a plane’s tail, sending signals from the flight control computer that can push the nose down or lift it up.