A single report of a miswired APU fire-extinguishing bottle on a Citation X (C750) has prompted a proposed AD to require placing identification sleeves on the positive and negative terminals of APU and main engine fire-extinguishing bottle wiring and reconnecting the wires to the correct terminal studs on Citation 500s, 550s, S550s, 560s, 560XLs and 750s. The fire-extinguishing bottles on these airplanes have positive and negative studs that are the same size, “so it is possible to cross-connect the wiring of the positive and negative leads,” the FAA said.