A gentle suggestion: whenever you get a locomotive, see if you can locate (in this case right on the manufacturers site) any owners manuals, wiring diagrams, exploded views, and schematics.
If you do this up front, it can help later, even if it is 10 years later.
In general, Bachmann has most of these for all their G scale stuff. At the moment the site is down, but here is the "entry" link
Greg