List the Lionel product number so that we can look up parts diagrams and other specifics to a loco to better help you. Otherwise- you get bare minimum from us trying to help
A short- is a low resistance electrical condition where something is shorting out the track or transformer power source causing high current and overload- at the same time- that short steals power away from the engine.
An open circuit- an engine has to pass power from the center rail pickups and then return it on the wheels with the power going through the engine. An open circuit- there is no load on the transformer or wiring, no current draw, the engine is simply not making contact and is not connecting the path.
Use a meter to check for continuity between each set of pickup rollers to see if wiring inside the engine is damaged. There should be continuity between all the pickup rollers. Also, the same test between wheels as similar wiring problems can exist between the trucks and wheels pickup, and depending on a painted frame to conduct current is not reliable.
Since your story and first post is slightly unclear- it's entirely possible you really did have a short at a switch and eventually this short without a good breaker in your power circuit, can burn up or damage wiring and traces in a loco between pickup wiring from each truck. So you might have started out with a short- and kept abusing it until it went open circuit.
Again, in a locomotive or even cars, with multiple wheels and trucks- it's entirely possible to have a short happen at one end, and the other end and all the wiring in between is taking huge short circuit current. Given enough abuse, this will then burn open circuit. Now you end up with only one pickup working and thus the engine stops at the smallest of gaps in switches or track because there is the bare minimum of pickup rollers or wheels connecting power.
