Pins shorted on Sparkfun RJ45 Magjack breakout

I recently purchased a sparkfun rj45 magjack breakout and wired it up but found that I didn’t appear to work. Upon further investigation it looks as though P1, P2 and P3 are all shorted together, in addition to P6, P7 and P8 all being shorted together.

I desoldered all of the wires from P1 - P8 (I didn’t wire up the LEDs at all) and inspected both sides to ensure that I hadn’t joined any pins with solder. I then did a continuity test between all pins again and got the same P1/P2/P3 and P6/P7/P8 shorted together results.

I never tested this before I started soldering anything but I can’t visibly see how I’ve caused this to happen, so I’m wondering if I got a faulty item. Appreciate any assistance you can provide.


Hi Allan,

Welcome to the forum!!

I’ve just tested one from stock and can confirm that the pins are shorted - this seems intentional(part of the RJ45 connector itself) as the MagJack breakout seems to be exclusively for use in an Ethernet system (to get communications to a microcontroller or SBC).

I’ll jot down a note so that we get the product page updated and make it cleared up for future makers.
I’ve just shot through an email so we can get your project back on track!



Thanks Liam!

I do apologise, but this breakout does in fact work just fine when wired up correctly for ethernet. I ended up doing some experimentation and found out how to make it work, and also possibly some additional information that could be added somewhere on the product page.

I think the biggest confusion with this breakout is that pins 1 to 8 would seemingly map directly to the 8 pins on the RJ45 connector, which is not the case. It was after reading the page about the mbed controller working with the breakout (mbed Starter Kit Experiment Guide - that I worked out that only the following pins matter:

P1 = Transmit+
P2 = Transmit-
P7 = Receive+
P8 = Receive-

To get this working, I connected the green and orange wire pairs to P1/P2 and P7/P8 and it worked perfectly.