I have been asked why 117 was incompatible with the FCPyF electrical system. Before the rebuild 117 picked up current via the loco and returned it via the tender. This is fine until you come to an electrical gap between two controllers, as happens at Bodjio.
Before rebuilding, (1) the loco and tender both on track controlled by Grande, picking up power via the loco from the red rail and returning it via the tender to the yellow rail. (2) Loco runs onto track controlled by Rio Paleta, the loco is now on the green rail there is no completion of the circuit to the blue rail because the tender is still on the yellow rail controlled by Grande. With the electrical circuit broken the train stops here and does not make it to (3).
After the rebuild (4) the tender collects and returns current from the red and yellow rails controlled by Grande. (5) As it passes over the electrical gap in the rails the tender collects and returns current from both controllers at once, making parallel circuits between red and yellow and between green and blue. This is not an issue providing the controllers are set for the same direction and a similar speed. (6) Tender collects and returns current from the green and blue rails controlled by Rio Paleta.
The train is now clear of Grande control so the terminus operator can either accept a train from the Resurreccion controller or carry out shunting work within the station limits.