I stripped a DB9 extension cable which I will use to connect to a DB9 connector on one end and an RJ45 on another. I need to make connections to pin 2, 3, and 5 on the DB9 side.

When I stripped the DB9 wire, I was surprised to find 5 wires, since there are 9 pins in a DB9 connector. Why are there 9 pins but only 5 wires?

One of the wires is unshielded. Why is that? The other wires are red, brown, orange, and black. Which pins do these go to?


5 Answers 5


I believe you are asking which specific wire goes to which specific pin, based on the wire color. If that is correct, I'll try to give you some guidance, but I must also warn you that although there is an accepted standard for wire colors on DB9 and RJ45 connectors, it is also common to find them with non-standard wire colors. So think of this as more of a rule of thumb, rather than a certainty.


1 N/C_Green_5








If this is not what you are looking for, please clarify and I'll try to help you.

  • \$\begingroup\$ Yes, that is what I was looking for. \$\endgroup\$ Commented Feb 19, 2011 at 23:46

It's very rare for all nine pins to be connected, here are the details. I only use three for anything I design - Ground, TxD and RxD. The other two will depend on the hardware and software.

  • \$\begingroup\$ Yes, I only need those three wires. However, how do I figure out which wire is what? \$\endgroup\$ Commented Feb 19, 2011 at 22:11
  • \$\begingroup\$ You will have to check against the hardware documentation. \$\endgroup\$ Commented Feb 19, 2011 at 22:12
  • \$\begingroup\$ I don't think you understand the question. I just want to know which wires in the cable are connected to which pins in the connector. \$\endgroup\$ Commented Feb 19, 2011 at 22:21
  • \$\begingroup\$ It depends on the hardware details of the system that the RJ45 is plugged into. You need the documentation. \$\endgroup\$ Commented Feb 19, 2011 at 22:50
  • 2
    \$\begingroup\$ @200ok404notfound - not sure there is any color standard. "when in doubt, ohm it out". in other words, it's easy enough to use the continuity-check setting of a dvm to match wire ends to pins, and then you know 100% for sure. \$\endgroup\$
    – JustJeff
    Commented Feb 19, 2011 at 22:51

There is no standard for the colours used to connect to a DB9 for serial data.

You can get away with using just TX, RX and ground sometimes.

The other pins are for controlling the flow of data via hardware.

The only way to find out what colour goes to which pin is to use a multimeter on continuity or a low ohms range.


What it appears to be is some kind of cable that someone connected a DB9 connector to one end and a RJ45 connector to the other. The cable in between could be any type of cable and have any number of wires. There may or may not be a standard involved with your cable.

You also don't need all of the 9 pins in order to have a functioning serial cable. Most have VCC, TX, RX, and sometimes CTS and RTS. That might explain the 5 wire you have.

Use a continuity checker to verify which wire goes to which pin.


I just had the same thing.

There is this cable which I've been using for about half a year now. I was convinced that it only had 3 wires. However, when I opened it today, I discovered it has 5 wires as well.

They are connected as follows:

Male side:

  • pin 1 = brown + also connected to pin 8
  • pin 2 = red
  • pin 3 = orange
  • pin 4 = yellow + also connected to pin 6
  • pin 5 = black

Female side:

  • pin 1 = connected to pin 8
  • pin 2 = orange
  • pin 3 = red
  • pin 4 = yellow + also connected to pin 6
  • pin 5 = black

I opened the cable because it was broken. And I noticed that the brown wire was disconnected on the female side. I assume that it needs to be connected to wire 1 though.

Well, the basic 3 wires are there and in right position:

  • pin 5 to pin 5.
  • pin 2 and pin 3 are crossed.

I had expected a simple loopback with pins 1,4,6 and pins 7,8 connected.


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