Some models of A4000 may have 26-pin header mounted on the motherboard, with a short cable connecting it to the serial connector. Pin 1 of this header is on the side closer to the power supply, and it shares the same pinout as the DB25 listed below (pin 26 is unconnected). Other models of A4000 have a high-rise, right-angle DB25 connector soldered directly to the motherboard.
Pin 1: Shield Ground
Pin 2: Transmit Data
Pin 3: Receive Data
Pin 4: RTS
Pin 5: CTS
Pin 6: DSR
Pin 7: Data Ground (Do not connect to shield ground.)
Pin 8: CD
Pin 9: +12V (20 mA maximum.)
Pin 10: -12V (20 mA maximum.)
Pin 11: Amiga Audio Out (Left)
Pin 12: Unused
Pin 13: Unused
Pin 14: Unused
Pin 15: Unused
Pin 16: Unused
Pin 17: Unused
Pin 18: Amiga Audio In (Right)
Pin 19: Unused
Pin 20: DTR
Pin 21: Unused
Pin 22: RI
Pin 23: Unused
Pin 24: Unused
Pin 25: Unused