Done!!! It works now like it should, idle increases when AC is turned on, then decreases when AC is off.

Nick, I did it pretty how you explained it above... I had a look at doing it in the boot near the ecu but was too much of a stuff around to find the right wires.
I'll post up pictures tonight :)
Now I just need to get a nipple welded on the BOV joiner.

Ok, so with all the effort Mrskylighter went to helping me fix this problem, it's only right I put up pictures on this problem was fixed. 
Problem: After conversion from a NA to a 1995 Gen 3 3sgte, the AC idle up did not work properly due to a difference in electronics between the NA and Gen 3.

• With the AC on, the idle dropped and the engine struggled (when the idle should actually increase).
• With the AC off, the idle increased and the engine revved slightly higher than it should.

Hence, the AC idle up was not working as it should.
(The following is credited to Mrskylighter and will only work if the negative is being switched, not the positive.  Also, for some strange reason the red wire on the AC plug was actually negative, and the black and yellow was positive).
 
This is the AC idle up (VSV) plug.

 
I cut the negative lead (in my case it was the red wire) and soldiered on about 200mm of wire to each side.  I kept the colours of the wires the same to avoid confusion.


 
Put some heat shrink on to cover up my dodgy soldiering haha.

Crimped the other ends of the red wires with some male connectors.

 
Stripped back some of the black and yellow wire (didn't cut) and soldiered on a piece of wire.  (Note: this was my positive lead.)  Couldn't heat shrink this one so I put some tape on.

 
Put a crimp on the end of that one and hooked them up to the 5 pin relay.



Red wire, ecu end - terminal 86
Red wire, plug end - terminal 30
Black and yellow wire - terminal 85
Earth lead to body - terminal 87a
 
I also put an earth lead on...you can see it bolted to the body on the right in the picture above.
 
Finally, made it look legit haha.

 
All works fine after plugging the AC idle up plug back in :)
 
 
 
 

All good mate. I'm getting the nipple welded onto my BOV joiner pipe this week so should all be back to normal.
Do the AC mod, took me around half an hour :)

P E T E
FYI - I'm not a fan of those crimp plugs. I have had them fail due to vibrations in the past. I'd recommend getting one of these wiring looms from Jaycar if you run into any trouble: http://www.jaycar.com.au/productView.asp?ID=SY4069
Its cheap and worthwhile!
 
This also stops you from incorrectly plugging all the wires back in if you ever have to relocate the relay!

Thanks PETE.  That does look like a good idea - I'm not a fan of using crimps either, prefer to solder and then heat shrink but in this case I had all of the materials at home and wanted to get it done fast.
 
I'll definitely keep an eye on it.