Electronic ComponentsGetting components/parts:I try to use circuits that have parts carried by Radio Shack, but they are slowly phasing out parts, and when you used to be able to buy a resistors in different values, often all you can get is an "assortment".Internet ordering is probably where you will need to go, try DigiKey or Mouser or All ElectronicsPolyswitchSometimes improperly called a polyfuse. These are self-resetting switches that will trip after a while, the mechanism is that the current flow generates heat, and if enough heat (current) is generated, the compound inside melts and becomes an insulator. Left to cool, the compound re-crystalizes and conducts again.The pro's include low cost, self resetting.The con's are that they keep trying to reset so under a heavy short circuit, you are not protected as well as a real fuse that opens up permanently, or a circuit breaker that must be manually reset.But they work well for our trains, and many companies use them, although seem to have been pioneered by Aristo-Craft.The ones Aristo uses are cheap, and often "false trip" because their "on" resistance is a bit high (that's why they are cheap).Aristo uses ones rated at 3 amps, and how fast they trip is dependent on the overload current.I have found inexpensive ones of superior quality and lower on resistance, so there will be less false tripping, wasting power in the component itself.These are a RUEF300-ND manufactured by Raychem. I bought them through Digi-Key and they were 35 cents each in quantities of 100.I use them on each power pickup lead from the motor blocks/trucks.See the article on the RS-3 for how to do and why. CL2 LED current regulatorsSupertex makes a 2 terminal current regulator that works up to 90 volts and allows a regulated 20 ma of current.