According to usb to db9 wiring diagram you will find only four wires used in the cable. The red one is for sure wire with dc ability of 5 volts.

Rs232 Rs422 Rs485 Db9 Amp Db25 Serial Port Pinouts And
Db9 wiring diagram. Generally pin 1 is marked on the front of the connector right next to the pin though you may need a magnifying glass to read it. An rs 232 serial port was once a standard feature of a personal computer used for connections to modems printers mice data storage uninterruptible power supplies and other peripheral. Pinout and diagram of de9 connector db9 connector commonly used for serial ports rs 232. Rs 232 maximum cable length the maximum cable length for rs 232 is 50ft but in practise depends on baud rate cable specific capacitance and ambient noise. Db 9 connector pinout null modem wiring diagram posted by circuit diagram in general circuits the term db9 refers to a common connector type one of the d subminiature or d sub types of connectors. Pinout of pc serial port rs 232 de9 and layout of 9 pin d sub male connector and 10 pin idc male connectorthis rs232c de 9 usually miscalled db 9 port is available in some pcs and many other devices.
Typically it utilizes black black red and white wire colors. These diagrams show the male grey background and female black background pin numbering for db9 and db25 sub miniature connectors. The red one is to get positive cable with dc ability of 5 liter. The dte pc has the male connector shown below and the dce peripheral has the female. Black wire serves as ground just like in every other device. In accordance with db9 to usb wiring diagram you will find just four wires used inside the cable.
The following schematic diagram show the male grey background and female black background pin numbering for db 9 connector. Typically it utilizes black green white and red wire colours. Black cable serves as ground just like in any other apparatus.