It sounds like the specs on your wall wart might be off. I found this post by gunrunner john in a different post. It spells out pretty clear what would be used to the aux power to your tiu. Again, look at what you are using now. Either it is wrong, or something might be amiss inside the TIU. Especially if you used the wrong one and possibly causing damage.
"Any power brick that supplies at least 2 amps and has an output voltage range from 12V to 20V will do. It can be either AC or DC, but most of the bricks I have happen to be DC. As for "where" on the label, it obviously varies by individual units.
Here's one I'm using, it happened to have the right plug to mate with the TIU. Note that it's 12V DC and plenty of power at 5.83 amps."
