I'm hoping the Aussie market Subarus are the same as the Euro market ones, so has anyone got a wiring diagram for a '98/'99 RHD EJ20 T Impreza? Any of those I've found on the new have been for JDM or USDM models and none match.

Have a look at the Subaru wiring diagram links in the Archive section at the top of this forum page. Here's the link
http://forums.aussieveedubbers.com/viewtopic.php?tid=14906