C,
If you want to power landscape lighting from your ET, all you need to do is add a 120 volt circuit breaker to your ET. Wire the output of the circuit breaker to the line (input) side of one of the unused relays and then wire the Load (output) of the relay into the power plug for the Landscape lighting control box (transformer).
Just to make sure we are both on the same page... There is NO transformer inside your ET that has anything to do with Landscape lighting...
Thanks,
Jim R.