Model Forum / General / Railroads / April 2007

You need a diode such as IN4001 inserted in the lead from the right hand
rail to the light bulb.
ASCII representation of the diode looks like ---[__[]--- wire leads on
each end of a small cylinder of black epoxy with a white band at one
end. The banded end should be towards the light bulb.
The diodes are quite robust and will withstand reasonable beginners
soldering but holding the diode with a small pointed nose pair of pliers
on the bare wire lead right by the diode might help.

Get some heat shrink tubing large enough to fit over the insulated wire
and cut a length big enough to cover the bare soldered parts.
Slide the heat shrink pieces over the wire before you start soldering
and when that's done slide the heat shrink over your join and run the
shank of the soldering bit gently over the heat shrink until it is
tight. It shrinks about 50%.

You want to end up with the diode and heat shrink somewhere in the loco
where it doesn't interfere with bogies turning, gears, body etc. etc.
Turn the loco around and do the other end.
If one contact of the bulb is to a metal chassis then you may need to
reverse one diode. (ie turn it around)

The worst that can happen if you get it the wrong way around is that the
light will be off when it should be on and vice versa.
Wrong wire? The loco will only go one way.
To much heat for too long? Wire insulation melts and causes shorts or
plastic chassis or motor bogie melts.

If you have to solder near plastic a wet tissue over the bits you don't
want to heat is useful.

Have somewhere arranged for putting the hot iron down safely and quickly
- unfortunately we humans usually only have two hands and one set of
eyes (generally focused on one spot) Soldering usually needs three or
four hands. ( two parts to join - solder - soldering iron - ...)

The tail lights will want a diode soldered from the same chassis lead
with the diode oriented the other way around ---[]__]---
Some bigger heat shrink tubing can go around the two diodes to hold them
together.
Last tip: melt some solder onto each of the leads you want joined before
attempting to join them, that way you only need to hold then together
and touch the soldering iron to the joint for about 2 seconds. BTW they
aren't joined until the solder solidifies ;-)

Regards,
Greg.P.