Adding a Tender Headlight

Electrically, this is so easy it doesn't need a schematic.  Mechanically, it's another story.  It's especially challenging if you want connectors between the engine and tender.

If you have a tender where the back comes off, make sure you don't make the wires so short that you can't get the back off the tender later to change the bulb.

Those locomotives where a permanent link keeps the tender attached to the locomotive do have it easy.  Just connect the blue and yellow wire from the locomotive to a grain of wheat bulb.

You can hot melt the bulb in place or any other way that suits you.  Use a rubber band to hold the bulb while you hot glue the wires.  Becareful if you use hot glue, because besides the obvious of touching your plastic model with the nozzle and melting it, hot glue is stringy.  I found that if you stop pulling the trigger and then hold the gun still for several seconds and then yank the gun back, it will break the string at the glue joint and not get on your model.

Connectors between the locomotive are challenging because they are "big" - in a relative sort of way.  Big is worse than just "out of scale."  The locomotive may derail if the joint isn't flexible enough.

Connectors that are not big, are very delicate.  So I've been looking at what is available.

Here is my first attempt.  It has the potential of being low cost and being small.

Scale Shops part #649-3420 is a two pin connector.  I suggest not using their pins; only their sockets.  Tin the wires from the tender so they just fit snug into the sockets - NOT extremely tight!  We now have a very compact connector.  I show some curls of wire inside the tender.  If the tinned ends break, you can cut and re-tin some new wire ends using the excess wires inside the tender.

Solder the sockets to the blue and yellow wires from the locomotives.  No, it doesn't matter which color wire goes to which lead of the grain of wheat bulb.  Put heat shrink over the socket.

Get the socket as reasonably close to the locomotive as you can.  No, this is not easy.  try stripping the wires before you poke the wires through whatever hole you found in your locomotive.  Be able to hold onto the insulation when stripping.  If you do not, you risk yanking the wire out of the decoder!

If this approach works appeals to you, you can get header strips from DigiKey (1-800-DIGIKEY).  They sell a strip of 64 pins for $2.89, part #ED7064-ND.  Digikey does have a minimum, so get a catalog and see what else they sell you would like before placing an order.