Cat5 wire connector does not appear to be continuous
Most devices in the last decade do not have plain RJ45 jacks. Due to micronization of components and the demand for smarter/smaller parts, RJ45 jacks have combined the Jack with the Magnetic Couplers that used to be separate parts.

Typical schematic for a Mag Jack:


That is a 2 pair, 100Base-T version. Some have the other 2 pairs connected to pins instead of shield. And Gigabit or 4 pair versions simply have 2 more sets of magnetic couplers.

Notice the IC next to this jack. That is an external magnetic coupler/transformer. If the router or device you pull your jack from does not have something similar, it most likely has a MagJack.: