>I notice it is lodged in
>/opt/trinity/bin/kpowersave
>is this right? note no '-trinity' after the executable.

That is right.
As for why it is not working, I can't say for sure. It may be that v3.5.13.1 and the wheezy kernel don't get along too well.
Have you tried upgrading TDE to 3.5.13.2? I think there are quite a few users of Wheezy and 3.5.13.2, so it should be easier to have feedback from them if you use the same version.
As for me I am running Jessie and TDE development version, where kpowersave is no longer used (actually it does not even build anymore in Jessie due to the lack of hal), so I can only provide some general comments/guidelines.

Cheers
  Michele