Installing Directional Lighting in Cab Units

[Desertdweller]

Many older model locomotives did not come with directional lighting.  It is an easy project to add this, and not expensive.

Today I added this feature to four of my N-scale Life-Like E units, but the principle involved could be used on any units not so equipped.  With a little modification of wiring, it could also be used on Bachmann units without directional lighting.

I started by looking inside a Con-Cor E-7 with directional lighting.  The headlight would only light up when moving in a forward direction. This is what I wanted.  The headlight bulb usually used is a grain of wheat bulb, but I have seen grain of rice bulbs used, too.

The diode used was marked "1100".  It was a small cylindrical diode, black in color, with a silver band around one end.  I found diodes identical to these at Radio Shack.
They are described as 1N4004 diodes, part number 276-1103.  They come two in a package for $1.19 a package.

The Life-Like locomotives used a plastic frame with roughly cast lead weights, but the conversion did not require any removal of material.

I found a spare grain of wheat bulb with thin black wire leads the same diameter as the leads on the grain of wheat bulb on the loco.  The forward weight is held on by a spring clip.  Pop the clip loose and remove the weight.  Some of these weights have been thoughtfully coated with an insulating coating.  Otherwise, apply plastic insulating tape down the slot in the top the wires go into.

On the right side of the loco, cut the headlight wire off at the frame.  Cut a piece of wire from the spare bulb about three inches long, and solder it to the contact strip on the frame where the other wire was cut off.

Put a 90-degree bend in the wire lead on the diode, in the lead that comes out the end opposite the silver band.  Cut the diode lead off just beyond this bend, and trim the new wire to reach the diode, then solder the new wire to the bent wire on the diode.

Fit the weight back on, and run the headlight and wires in the insulated slot.  With the bulb in place, snap the clip back in place.

The diode must have the silver band at the end facing the headlight.  Trim the other lead on the diode to about a quarter-inch, then shorten the unattached wire from the bulb and solder it to the forward lead off the diode.

Before installing the body, test this on the track.  You haven't messed with anything in the drive train, so it should still run fine.  The headlight should come on when the chassis is moving forward, and go off when backing up.  If the opposite happens, you have installed the diode backwards.  If the headlight shines when going both directions, you have a short between the diode and the headlight.  If the light stays dark in both directions, you have a bad solder joint at one of the three places you soldered.

Why this works:  diodes are a one-way only gate for electricity.  Since direction in a DC circuit is determined by polarity, you are only letting power reach the headlight when the current flow is in the direction for forward movement.

What you will need: 

Radio Shack 1N4004 diode.

Pencil-type soldering iron and thin solder.

Small wire cutter.

Needle-nosed pliers.

X-acto knife (for stripping wire).

Small screwdriver (for popping off clip).

Electrical tape.

Short length of very light insulated wire.

I haven't tried doing this with a bi-directional hood unit, but it should be an easy conversion using two diodes.  Just remember to keep the silver band on the diode at the end facing the light bulb.

Les