Represented is the 2006 release of the Atlas U23B locomotive. There are three options for a decoder installation. The A4X decoder is a drop in replacement. The T1 or MC2 decoder with a short harness are other options. Pictured below are the MC2 and T1 decoders installed with short harnesses.
MC2P-SH decoder. (MC2 decoder with a short harness).
T1P-SH decoder (T1 decoder with a short harness).