It is not always valid to test a resistor in a circuit because you are also measuring the resistance of the circuit that they are a part of so the resistor is in parallel with other devices, you are also measuring the resistance across them as well and the measured resistance will always be lower than the lowest device in the parallel connection. To get a true measurement of the resistor, you would have to remove one end from the circuit to break the link to other devices in the circuit. There is a separate link to the MAGjack in the WIKI right under the BOM for the EDT. It is a link to Newark, not Mouser.