SAND PAPER HAS NO PLACE WITH TOY TRAINS make sure you have all the pins in the track.. you can get contact cleaner and wipe the track down with that or lightly use a pot scrubing pad and LIGHTLY USE THAT
The power supply supplies from 16 to 18 volts AC to power the train and the accessories such as your lamp post. Just remember those old trains ran on AC power and NOT DC. Use needle nose pliers to squeeze the track ends together so the pins won't just fall out.
It is actually track conductivity issues I think. I have been through this before and used a brand new, replacement engine with coal car to eliminate that variable. The track sections and pins were just dirty and corroded. I separated all of the connective pins from the track and gave the track and pins a warm; about 200°F, citric acid bath. I still had to hand clean at least half of the pins. I chucked each pin into my drill and spun against a 99% (I think 91% would suffice) alcohol-soaked scotch-brite pad.
the worst thing to use is sand paper you are taking all the tin plating off the track for one thing.. second the grit will get in the workings of the train....and you are distroing the center contact... .....