Track Modification for Auto Reverse Unit

In order for the Auto Reverse Controller (ARC) to sense when an engine or trolley reaches the end of the track an insulated section of track must be installed near each end.  When the train enters this section is stops and the ARC senses a drop in voltage and knows where the train is.

In order to get the train out of the insulated section a diode is placed across the cut in the track.  Diodes only conduct in one direction.  When the train enters the diode section it comes to a complete stop.  When the ARC reverses the polarity to bring the train out of the section the diode conducts and the train operates again.  The photo above shows the correct wiring for an HO layout.  Note that the diode has its band to the left.  For a G scale layout the diodes must be installed with the opposite polarity, that is with the band on the diode to the right as in the drawing below.


Diodes are available at Radio Shack.  Make sure you get ones with a high enough rating to handle the power drawn by your engine.  A small engine will work well with a 1 amp diode.  Larger motors in larger engines may need diodes with a 2 or more amp ratings.



1N4003 Micro 1-Amp Diode 
Catalog #: 276-1102


4 Rectifier Diodes  6-Amp
Catalog #: 276-1661


Quick Self Drilling Self Tapping Screw Method

While experimenting with ways to mount diodes in large scale track Bob Groover and I stumbled upon what may be the best way to quickly mount diodes.  All that is needed is an electric drill and self tapping / self drilling #6 screws.  These screws, pictured with a #6 stainless self tapping screw, will drill and tap a hole in LGB or AristoCraft track in a jiffy.  The stainless steel screws are used for a permanent installation as they will not rust.


Mark the rail for screws based on the size of your diodes.  Start the screw with an electric drill holding a Phillip's bit.

Push hard and the screw will begin to drill into the brass.

Let it go all the way in so that it threads the hole, too.


Drill the 2nd hole.

Using an abrasive cutting wheel in a Dremel cut the trail between the screw holds.

Be careful not to cut the plastic below the rail.

Bend the diode's wires so that tightening the screws will pull the leads tighter.  Tighten and trip the leads.

Replace the  self drilling screws with stainless steel if you will use the track outside.


Cut off inside the rails with the Dremel.



two pieces of track, two 3 amp diodes, 3/32" brass tubing

bend diodes

use diode to mark track for holes

remove rail from ties

drill 3/32" hole for brass tube

clean and flux all parts

wrap solder around brass tubing

heat with propane torch from below

let solder flow

almost done

insert diodes with proper orientation

solder with hot iron, not torch!

cut track between diode connections

reinsert in track - may be touch getting past some plastic protrusions

super glue piece of cable tie between rails for insulation

epoxy below rails to hold firmly in place