MTH TIU trips my MTH Z4000 when power is applied. This unit has never been used to run trains, software upgraded to 4.20 in 2009 & 4.3 in 2015. Bought in 2004 from a now closed local train shop to use in the future. I am now in process of building a layout, got the TIU out to test. Hooked it to a Lionel ZW-L also and as soon as you apply power the breaker trips which I assume is indicating a short in the TIU. Would the TIU allow software upgrades to be installed if it were defective out of the box new, or during the sw updates, could the update process have caused this problem?? Wires connected correctly. Both transformers also new and work to run trains. Any suggestions on anything I can do to correct the issue OR would it be worthwhile to contact MTH service OR should I bite the bullet and purchase a new one? Do the newer TIUs have different connector for the Wi-Fi unit? Thank you for any help??