The FL9 was a critical locomotive for operations out of Grand Central Terminal in New York City. Originally operated on the former New Haven lines the fleet's operating area spread under Penn Central and Conrail/MTA to include the former New York Central lines north along the Hudson River.

With no direct replacements on the horizon, in the 1980s the decision was made to rebuild and upgrade many of the original FL9s. Rebuilding typically included the addition of HEP (Head End Power) to replace the older steam heat boilers, as well as upgraded braking systems and electronics. These rebuilds were done in several batches for Metro North and Amtrak.

Notable among these rebuilt units were those which were sold to the Connecticut Department of Transportation and were rebuilt by Morrison-Knudsen in 1984-85. Owned by ConnDot, they were operated by Metro North. The units re-entered service wearing their original "New Haven" black, white and re