How to detect the 9-pin interface of computer

I use the old machine control LED and a 9-pin interface. Now I can't connect the LED. Want to know how to detect the interface number? The 9-pin interface used for old machine control should be RS232 interface. It is a serial interface. The easiest way to detect the quality of 9-pin serial port on the machine is to find a serial mouse and open it.

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