Nothing obvious to me in pics at issue. But I would ask you to look closely at a couple of things noted in pic by red arrows:
1) the bulb socket to see if there's anything in there causing a short, it seems there's some black substance on the outside of it.
2 ) where the black wire passes through the smoke stack bracket to see if wire insulation is damaged
A couple of additional suggestions if the above check out:
If the smoke switch is on, try turning it off
Re-install wheel linkages and then try running the loco without it's shell installed.
Would also suggest when testing above, preferably in low ambient lighting, to look for any sparks inside the loco.