This is an update of an article I wrote back in 2010 or so on how to make your own resisted wheel sets..
Current-sensing block detectors can be used to detect the presence of a train within a given electrically isolated block on a model railroad layout. As implied by their descriptive name, they work by detecting the presence of current flow between the two rails. Typically locomotives and lighted rolling stock such as passenger cars are the only current-users riding the rails. A small resistor connecting two metal wheels that share the same axle, will cause a minute amount of current to flow between the two rails. This small current is enough to be sensed by the block-detector.
This article details how I made my own wheel sets. Arguments have been made for alternative resistor values. While placing two of these 10K wheel sets per car (1 wheel set per truck) works flawlessly with my Lenz block detectors, you may find you need to experiment with alternate resistor values depending on your circumstances. Update 2016: I have since reduced this to one axle per freight car with perfectly fine results.
Update 2016: Originally I used Proto 2000 wheelsets with plastic axles, but later discovered that Intermountain wheelsets with metal axles. The metal axles negate the need to paint the entire axle with silver conductive paint, as the axle itself conducts electricity.
If you still have one, one of the Proto 2000 plastic packaging fronts works as a great holder for your wheelsets. This will work with both the Proto 2000 and the Intermountain wheels. I typically open a package, then apply a very small amount of cyanoacrylate adhesive (a/k/a Super Glue) near the center of each axle.
Update 2016: When using the Intermountain wheelsets, mount the resistor so that it is positioned in the corner, over the insulator, where the axle meets the wheel. Be sure to mount the resistor on this insulated side. See illustration.
Next, carefully separate the “ammo tape” or “filmstrip” to allow four resistors to fall out of their packaging. Using a pair of tweezers or a small screwdriver, or whatever works for you, carefully pick up one of the resistors, and place it on the axle where you have applied the small drop of cyanoacryllic adhesive. Be sure to place the resistor on the axle so that the numbered side of the resistor is facing up, away from the axle. I’ve found that placing the resistor upside down on my fingertip and then bringing the axle to the resistor works really well. Avoid getting glue on the resistor contacts, which are the silver strips located on the resistor’s numbered (top) side, along the two shorter edges. Allow the glue to dry. (The glue can act as a solvent for the paint, causing it to run together beneath the resistor, so be sure the glue is completely dry before applying the paint.)
Now you’re ready to apply the conductive paint. I’ve been using the applicator included with the paint, but you could probably use a very small brush or a toothpick, too. Apply just enough paint to adequately bridge the contacts to the axle, and the axle to each metal wheel. Use a magnifying lens if needed to make sure you have a continuous bead of paint. (As stated earlier, if you use wheelsets with metal axles, mount the resistor in the corner and only use enough conductive paint to connect the resistor to the metal surface of the wheel and to the metal axle.)
The conductive paint does not conduct while wet, and until it dries completely, may give you erratic and false readings. After the paint has had time to dry (typically 5 to 10 minutes), check the resistance of each wheel set by touching the leads of your meter to each wheel pair. You should get a reading of about 10 K ohms if the paint is dry, and you have a continuous circuit.
Some modelers paint the completed assembly with a non-conductive black paint to help hide the resistor.
Just one resisted wheelset per piece of rolling stock creates enough resistance to work well with the Lenz LB101 current-sensing block detectors I use on my layout. You may have to experiment with one or two depending on your set-up.