The question on how to add a motor to the 10173 Holiday Train has come up through the ILTCO Feedback link a couple times this holiday season.? LEGO sells a kit which combines the 9v motor and the 10173 Holiday Train but the included instructions don’t show how or where to add the motor.? I ran into this myself when we set up the NCLUG tree at Tinsel Town.? I knew I’d seen this done somewhere but I was in a bit of a rush when I set up the train so I replaced one of the bogies on the passenger wagon with a motor and removed the undercarriage and was good to go.? This isn’t a great solution and when I got the most recent e-mail asking how to do it, went searching for the correct answer.
It turns out you can download instructions from LEGO.com to modify the tender with the 9v motor.? I found this information in this long thread discussing the Holiday Train on LUGNET.