I have this second hand engine that would sit on the track, headlights on but no movement. This is the second of such an engine I had this experience with. So what I did was decide to investigate. First, I gently took off the body. Second I did a quick inspection, for burnt marks for example. After seeing that everything was normal, I then separated the board from the engine. This was done with one small screw. After that, I looked at the gears and cleaned them while at the same time inspecting each tooth of each gear as well as all of the contact plates. All seemed normal and so I then moved on to removing the motor itself. From my past experience, I knew the bushings could be worn down not conducting a good, “clean” electrical circuit. I carefully removed them while looking at the carbon buildup on the contact points of the shaft. I cleaned them, inspected the statum, wiring and “looseness” of the motor and shaft. After seeing a relatively good looking engine, the only thing left for me to do was flip those carbon bushings. I then put the springs back in along with the cover and slid the engine back inside. I then put the engine back on the track, gave throttle power, saw the lights turn on again and, viola, the engine moved.
This took literally only a few minutes and was actually kind of fun.
Now this may seem simple, and it is, but it also saved me between $250 and $300 because I was looking at buying a brand new engine. One thing to remember – keep that track clean – very clean.