RJ-45 with only four wires?
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