Thanks to all for responding!
Tom, I honestly don't know enough about motors (yet) to tell you what the Geep is running, but here is a diagram from Lionel:
A/F GP-7-9-20 Units - Pictorial Diagram
Of course, I'm an Android user, though I have the LionChief app that will run the Polar Express unit. I haven't tried the Legacy unit yet.
Rich, I'll look up the Blue Rail info, thank you!
All, I spoke with a friend that works for Lionel. He spoke to Dave Olson about the Geep, and he replied:
"We make the GP in FlyerChief, so he could get a LCP1 board from service and make it FlyerChief like his Polar Express engine. If he wants TMCC, he would need to upgrade the engine with Electric Rail Road boards. http://www.3rdrail.com/err-3rdrail/ I would suggest a cruise commander M. and if he wanted sounds, he would need the sound commander, though I don’t know if it’ll all fit in such a small engine."
So that's another option, I suppose. I just don't know enough yet about rigging the setup, but I'm reading daily.
