Is it an SD-35? What is the product number? Doesn't it have the TAS EOB system factory installed?
http://archive.atlasrr.com/OLoco/arc-osd35.htm
TMCC Features:
- EOB™ Speed control technology
- Lionel TrainMaster Command Equipped featuring RailSounds™ digital sound system (including horn, bell diesel-roar sounds, etc.); Crew Talk (in command and more...
- RailSounds™ operates in both conventional and command modes in 3-Rail.
- Operating electro-couplers