MC2 micro decoder with S1 harness fits very nicely using original NMRA socket supplied with the loco.  The diode light board has been removed and the 2 volt bulbs replaced with 12 volt bulbs. The body shell fits on no problem with room to spare!  The MC2 decoder can be ordered together with the S1 harness (MC2P-S1) or the harness is available separately (MC-S1).