I have spent some time time trying to get the extruder board up and running. I hit a few snags along the way, and thought I would document them in case it helps anyone else.
Firstly is uploading the firmware, as with the motherboard you can use jumpers if you are unsure of your 10 pin cable, just make sure you get them correctly aligned, they are the opposite way round to the mother board so you have to put the extruder board on its back if you want to do it this way. First problem I had was getting the arduino software to correctly upload the firmware I was starting to think there might be a problem with the board. After a bit of looking on the Internet I saw many comments about pressing the reset button just before upload, I tried this and after a few attempts it worked! I was amazed. What I had to do was hold the reset button down, click upload, wait for the text to appear then let go of the reset.
The next was the wiring, i was baffled at first by how to set it up, there wasn't many clear instructions, but I did stumble upon the "official" guide which is hard to find (here is the link). On this site it shows a picture of how it is wired up. I copied the wiring and got some action when I tried starting the RepRap software, except to start with I was getting zero readings on the temp. It took a few attempts to get everything working, I'm not sure what I changed but it seemed like the boards needed to be started in the correct order, and having good solid wiring certainly helps, I've started using some premade jumper cables rather than the IDC connectors.
The extruder stepper now steps when i click extrude, and the thermistor is reporting the correct temperature. The only annoying problem is that the stepper makes a high pitch whine whenever it is not stepping, I tried trimming the pot down and it didn't help, just stopped the stepper from turning. I tried switching to the software PWM set current bypassing the pot but it didn't help either. I've been tracking the temperature and the stepper isn't getting hot so I'm not worried, but the noise is annoying. See below for a video of the setup printing the minimug.