Dig through a junk drawer, I find a long cable with RJ-45 on each end.  Definitely not RJ-11.  It has only four wires.  What might it have been used for?

I'm not expert on wired ethernet, but in forty years of tech work, I've seen only six and eight wire connectors, mostly eight. This is the first time I've seen four on RJ-45.

  • \$\begingroup\$ RJ-45 with 4 pins only, or RJ-45 with 8 pins, but only 4 are connected to the cable? \$\endgroup\$
    – AndrejaKo
    Jul 2, 2019 at 19:47
  • \$\begingroup\$ role of sush a cable depends on the wires order it can be serial (not ethernet) use for example but using rj45 plugs, it can be tokenring it can be many things look at google image with "rj45 4 wires" search maybe \$\endgroup\$
    – user201301
    Jul 2, 2019 at 19:52

1 Answer 1


For ethernet networking up to 100Mbps only 2 pairs are used, so you can (fully outside specs, but working) wire 1 pair to 1-2 pins and second pair to 3-6, and it will work.

Some people in old ages, even have used one ethernet 8 wire cable to drive 2 connections by splitting the wires in 2 connectors in each node.

Fully outside any reasonable spec, of course

  • \$\begingroup\$ I didn't check the positions carefully, but three adjacent to one end and the other not quite to the other end sounds about right. The desk the drawer was in had an ancient Windows box on it. (Ancient as in expecting PS-2 mouse and keyboard.) \$\endgroup\$
    – WGroleau
    Jul 2, 2019 at 20:24
  • \$\begingroup\$ Exactly, 1-2 for the green pair and 3-6 for the orange one. \$\endgroup\$
    – avelo
    Jul 2, 2019 at 20:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.