What do you mean "where does this link go?" As I say it points to a simple world to reproduce the bug.
I did search before posting, but couldn't find anything similar to this problem (only bottom of Energy Link not working in SMP).
I'm not sure what you mean by "build craft has not been updated so it no longer works". If I'm correct Tekkit 2.1.1 uses Buildcraft 2.2.12, IC² 1.71 and PowerConverters 1.3.1_01 which are all the latest versions available for Minecraft 1.1.
If I run a vanilla server with those mods (same versions) the Energy Link works perfectly so it is definitely a Tekkit bug.