Given that more manufacturers are using the RJ45 connector for RS232 it makes sense to have a standard. The table below shows various different standards discovered. The Pair Numbering and Color Coding is as for the 258A Standard for wiring of Cat 5 cable. The assumption being here that you want to run Cat 5 for Ethernet but use it also for RS232 if required. Of all the 'standards' found, the first and oldest one (Defined by Western Electric as their WE8W standard) makes the most sense because Pin 1 (TXD) is twisted with Pin 2 (Signal ground) and Pin 5 (RXD) is twisted with Pin 4 (DCD - which is at a static potential when receiving data).
RS232 signal names are for the device with the RJ45 connector behaving as a DTE (Data Terminal), being connected to a DCE (Data Comm Device - Modem) and a right pointing arrow -> meaning an output
| 258A Wiring | Pin | RS232 #1 | #2 | #3 | #4 | #5 | #6 | #7 | #8 | ||
| DTE | DCE | ||||||||||
| OR Pr 2A | 1 | TXD | ---> | Input | DCD <- | DTR -> | RNG <- | RTS -> | RTS -> | TXD -> | |
| OR Pr 2B | 2 | 0V | <--> | 0V | RTS -> | DCD <- | DCD <- | DSR <- | DTR -> | RXD <- | |
| GR Pr 3A | 3 | DTR | ---> | Input | 0V | CTS <- | DTR -> | DCD <- | TXD -> | RTS -> | |
| BLPr 1B | 4 | DCD | <--- | Output | TXD -> | TXD -> | 0V | RXD <- | 0V | CTS <- | 0V |
| BL Pr 1A | 5 | RXD | <--- | Output | RXD <- | RXD <- | RXD <- | TXD -> | 0V | DSR <- | RXD <- |
| GR Pr 3B | 6 | DSR | <--- | Output | 0V | RTS -> | TXD -> | 0V | RXD <- | 0V | TXD -> |
| BR Pr 4A | 7 | CTS | <--- | Output | CTS <- | 0V | CTS <- | DTR -> | DSR <- | DCD <- | CTS <- |
| BR Pr 4B | 8 | RTS | ---> | Input | DTR -> | AUX | RTS -> | CTS <- | CTS <- | DTR -> | RTS -> |