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Just like the WTIU, the TIU can be connected to the Lionel Base 3.
The TIU can be connected to the Base 3 using the TIU/TMCC-Legacy Connector Cable 50-1032, the Lionel SER2 and the Lionel LCS PDI Cable (6-81501 or 6-81502). Connect the TIU to the SER 2 using the TIU/TMCC-Legacy Connector Cable 50-132. Then use the Lionel LCS PDI cable to connect the SER2 to the Base 3.