Dell PowerConnect 7048
Even though this is about a Dell PowerConnect 7048 Switch, it applies to a huge range of their switches in the PowerConnect series including the 2700, 2800, 3400, 3500, 5400, 5500, 6200, 7000, 8000, and 8100 series. It is not a step by step article on how to configure the device. This article is only about the cable. And the reason I'm writing this is because there was so little information available to me about the cable pin outs. Everyone wants to sell you a cable, but hardly anyone has information about the cable itself.
If you've purchased one of the above devices off of eBay the device probably is not set to factory defaults. And odds are the seller has no clue about the device at all, other than what they can sell it for. How do you know what the user name / password is, IP Address, or how to reset the unit to factory defaults? The answer is you have to connect into the device with an old fashion serial / terminal connection. Again, this is not a step by step on how to do that and is only focused on the cable.
I will give you a couple of hints if you want to reset it. Once you're in the boot menu, select item 10 to reset it to factory defaults. And after it is reset, be patient during the next boot. Wait for the "wizard" to appear and set the user name / password and out of band IP Address. Once that's done, you can access the device with a web / GUI interface by connecting the "out of band" port to another switch or directly to a computer.
In short, the cable is an "RJ45 rollover cable" (https://en.wikipedia.org/wiki/Rollover_cable). Technically RJ45 is not correct in this case, 8P8C is the correct term (https://en.wikipedia.org/wiki/Modular_connector#8P8C). It's the same cable Cisco uses to connect to most of its routers.
Useful information about the serial port settings: https://www.dell.com/support/article/us/en/19/how11279/dell-emc-networking-default-console-settings-for-powerconnect-x-series-n-series-on-series-chassis-series-s-series-switches-z-series-switches?lang=en#PowerConnect%C2%A02700280034003500540055006200700080248100
Pin out Information;
DB9 8P8C (RJ45)
1 Not Connected
5 4 and 5
9 Not Connected