I finally found out more about the connectors. The are called IDC MTA-100 and they are blue and red because that's the color code for 22 AWG (red, for the resistor) and 26 AWG (blue, for thermistor) wire.

If like me you just need the blue and red connector for the hot-end you need these part numbers:

3-640440-2 the red one for the resistor
3-647002-2 the blue one for the thermistor

Just google the part numbers and you will find them on digikey or elsewhere (I'm ordering them from RS-Components).

You were a MASSIVE help!
Just ordered mine from mouser...bought a total of 6 for $14 with 3 day shipping.

I also ordered a heater resistor (well, 10 of them) I think could be compatible with the Solidoodle hot end.

I finally found out more about the connectors. The are called IDC MTA-100 and they are blue and red because that's the color code for 22 AWG (red, for the resistor) and 26 AWG (blue, for thermistor) wire.

If like me you just need the blue and red connector for the hot-end you need these part numbers:

3-640440-2 the red one for the resistor
3-647002-2 the blue one for the thermistor

Just google the part numbers and you will find them on digikey or elsewhere (I'm ordering them from RS-Components).

Great find, I dislike how rs-electronics have a minimum order of 10. And Digikey charge a flat $34 shipping :s

I finally found out more about the connectors. The are called IDC MTA-100 and they are blue and red because that's the color code for 22 AWG (red, for the resistor) and 26 AWG (blue, for thermistor) wire.
If like me you just need the blue and red connector for the hot-end you need these part numbers:
3-640440-2 the red one for the resistor
3-647002-2 the blue one for the thermistor
Just google the part numbers and you will find them on digikey or elsewhere (I'm ordering them from RS-Components).

Thanks!  I will pick those up. 

FYI, for anyone who is interested, hotends.com has the J-Head MK V in stock right now.  They re-stock their inventory around noon on Friday and ship on Monday.  I picked up one of their extruders to replace the stock one.

If like me you just need the blue and red connector for the hot-end you need these part numbers:

3-640440-2 the red one for the resistor
3-647002-2 the blue one for the thermistor

Just google the part numbers and you will find them on digikey or elsewhere (I'm ordering them from RS-Components).

Thanks to the ebay comment here I just ordered two j-head mk v's from the UK. If the resistor dies in the future I can simply replace it myself without begging Solidoodle to tell me a part# or waiting around for a replacement and shipping broken parts around half the globe.

The only thing I still don't know is a part# or "name" for the wire connectors used by Solidoodle. Could anyone help with that?

I just noticed something is wrong with the plexi of my extruder. What's going on there? (see picture)

I really hope having the nozzle + brass rod thing in acetone over night solves the clog and i can at least print the mk4 extruder before the plexi breaks.

nothing is "wrong" persay with the plexi.

those cracks are just what happens.

it's because they guys as solidoodle chose to make the extruder from acrylic rather than something less brittle, (say lexon, or ABS) as a result, the clear acrylic tends to start to fracture, eventually it cracks.

There isn't a lot that can be done.
short of buying a new head from Solidoodle, or printing one of the jigsaw replacement heads that are uploaded to these forums.

I checked out their website, and I like that extruder, but it is out of stock.  Anyone know where I can find something equivalent?  Or when they might get new ones?  I have Lawsy's MK4 mount, so preferably, it would be something that works in that.

There seems to be quite a few MK IV's on ebay. As it is a relatively open design anyone can produce it as far as I am aware.

I have just printed lawsy's MK4 mount. So will be test fitting the MKIV extruder when it arrives and will  modifiy this mount if necessary.

Ordered yesterday, shipped this morning.  I almost forgot what that feels like, haha

The J-Head is really good - www.hotends.com.  The dimensions of the mounting groove are slightly different, so the MK4 might take a bit of sanding to get it to fit.

I checked out their website, and I like that extruder, but it is out of stock.  Anyone know where I can find something equivalent?  Or when they might get new ones?  I have Lawsy's MK4 mount, so preferably, it would be something that works in that.

I am having the same issue with clogging and skipping these days.  It all started with a stringy print when I was using Octave's Black filament, and soon the extruder motor was skipping.  I unclogged the hot end, but the problem seemed to persist.

One thing I noticed is that the extruder works decently well if it is just hovering freely above the platform, but if it is printing the second layer, it almost instantly skips and clogs up. 

In my case, there are a few issues that might be to blame:

1. I didn't screw the brass fully into the PEEK since it wasn't hot at the time (maybe the filament doesn't properly enter the brass tube?

2. I accidentally drilled out a bit of the PTFE liner at a small angle, so the filament might get stuck on the walls

3. The nozzle might not have been fully unclogged.

Clearly, I made quite a mess of it, so it seems that replacing the extruder and/or the PEEK is going to be necessary in the end.

The stringy/wispy extrusion also had a strong tendency to curl. After a while the pressure would build up causing the extruder to skip.

I removed the hot end, took it apart. Cleaned out the nozzle as well as I could, including a slight drilling of the inside of the nozzle as I could see some black substance. Got a small print out, but then same stringy result. Went to strip it down again, but this time it was really bound up and I smushed some threads with my vice grips trying to remove the nozzle.  Frustrated ordered myself a new J_Head MK-IV.

So today, feeling a bit better. Stripped down the hot end again. Used my tap and die set to rethread the barrel. Soaked it all in acetone for a while. Reamed out the barrel with a drill bit and some other engraving/crowning like tool.

Once I had managed to clean it to the point I could see light through the nozzle. I placed it under my microscope that has an attached webcam and took some pictures:

So as you can see, it is about half clogged, with a black substance. I used a fine sewing needle and swished it around in the hole, and then took some pictures again:

Now it is an almost completely clear circle, and have managed several small prints without clogging.

The acetone helped a bit. But what really helped was drill bit with a diameter that fitted. I carefully drilled out quite a lot of white plastic from the sides and from the nozzle end. I'm not sure if I got 100% out but after several baths in acetone and more cleaning there was no plastic coming out of it. I still couldn't remove the nozzle from the threaded rod/pipe thingy though. So, who knows.

Right now I'm printing something and it seems to work fine.

Thanks for all your help!

What I learned: I will definitely need another hot end for ABS. I just don't know if it's better to buy a second one from Solidoodle or to buy two new J-Head hotends.

Also: Will the MK4 extruder work if I print it in PLA? with it's lower melting point and all.

I really hope having the nozzle + brass rod thing in acetone over night solves the clog and i can at least print the mk4 extruder before the plexi breaks.