The very very first was Rev G. Unlike those that followed, it didn't have an internal fuse and all black terminals were connected internally. Also, wires were soldered to terminals, not held by nuts. As initially delivered, they had a bad circuit. MTH fixed them under warranty and, at least for me, I have had no further troubles.
As to your problem, I suggest opening up the TIU case and checking the nuts that hold the wires to the through case screw terminals. All of my TIUs, except the Gs, were loose. I added an internal star washer and another nut to lock them tight. Nut is metric, and stocked by Ace. Sorry, I don't have the size right at hand.
