One thing to watch out for when running postwar operating cars with modern locomotives that contain electronics, is voltage spikes. When a solenoid is energized there is energy stored as magnetism. When the voltage is interrupted this energy is released as a voltage spike. Spikes as high as 100 volts have been recorded on Lionel layouts. Model train people protect against this by installing TVS (transit voltage suppression) diodes. The best place for these diodes would be in the loco needing protection. Next best place would be across the two wires going into the solenoid coil. The easiest place to put them is between the center rail and outside rail. This can be as simple as connecting the two wires on the TVS to the two terminals on a lock-on and just snap in onto the track. No other wiring is needed. I like to use the LCS, lighted lock-on, as the light bulb also will absorb additional energy. A typical TVS recommended on this site is from Mouser, (Little Fuse) 576-1.5KE36CA. When a device like this sees a excessively high voltage spike, it shorts the two wires it is connected to together converting the voltage spike to heat. These devices are cheap, maybe less than $1 each.
There has been lots of discussion on this site over the years. Use the search engine and search for “TVS”. One of the early documents on this problem can be found at the following thread:
https://ogrforum.ogaugerr.com/...tage-spikes-and-tvss
