When the model railroad locomotive’s motor briefly loses contact with the track while in motion, it will emit a voltage pulse. A protective diode (rectifier or LED) will prevent the pulse from reaching the LED. Generally, the rear light will emit brief flashes when the locomotive is moving forward. A small ceramic capacitor connected directly across the LED will short circuit these high frequency pulses.

R1 = Current Limiting Resistor C1 = Antiflicker Capacitor D1 = Reverse Protection Diode D2 & C2 = Peak Hold

R1 (for .3 A @ 8 volts track) = 1.5 KΩ, 1/4 W C1 = 3.3 m F / 6.3 V C2 = 1.0 m F / 25 V D1, D2 = 1N4004, or similar