Adam, sounds like your having a few dramas.
First thing stop!

Do not connect power!

Disconnect transformer.

Sounds like you have somesort of short circuit, probably a dead short or near dead(very little resistance)

Put your multimeter on continuity test.
Follow cables and test each pair of wires coming out of the transformer. And follow there path, away from the transformer, until you find a short or near short value.
Take pictures of anything you disconnect , so you can put it back together the right way.
I think you should be able to find the problem, without powering it up. If it is a failed device thats shorted.

Good luck.