MODELING MARS LIGHTS ON CGW F-UNITS David Webb In the pre-ditch light diesel era, the Chicago Great Western, as did many other, but not all, roads, specified dual headlights on its cab units. I gather that the main purpose of the upper headlight (actually two Mars lights) was "to be seen," i.e., for signaling other trains, to be more conspicuous at grade crossings, etc. The main purpose of the lower was "to see," i.e., to illuminate the track ahead. Use of the lights was governed by Rule 17: "TRAIN SIGNALS "17. The [standard locomotive] headlight [lower light] will be displayed to the front of every train by day and by night. It must be concealed or extinguished when a train turns out to meet another and has stopped clear of the main track, or is standing to meet a train at end of two or more tracks at a junction "S-17 (B). When trains meet within Centralized Traffic Control limits, and it is not necessary to stop for opposing train, headlight will be dimmed instead of extinguished when on siding "OPERATING INSTRUCTIONS FOR MARS COMBINATION WHITE AND RED FIGURE "8" HEADLIGHT
"17 C. White light. "To be used in figure "8" position whenever the standard locomotive headlight is in operation at night. "Red light. "ON SINGLE TRACK - When head end protection is required as provided by Rule 99, enginemen will immediately display RED HEADLIGHT When occupying main track meeting an opposing train, RED HEADLIGHT will be displayed approaching and while standing on main track awaiting arrival of opposing train. "ON TWO OR MORE TRACKS - [Under various circumstances which might result] in fouling adjacent tracks, or when necessary to provide protection doing station work, enginemen will immediately display RED HEADLIGHT " In all cases, approaching trains would have to stop immediately were the red Mars displayed. After the infamous merger, C&NW discontinued use of the Mars lights, and the upper headlight openings on the cab units were plated over. Modeling notes: Using a sophisticated decoder such as the Train Control Systems A6X, it would theoretically be possible digitally to control the headlights exactly prototypically. However, the physical modeling challenges of trying to do so, certainly in HO or smaller scale, would be, to say the least, daunting. One would have to use very small red and white LED's or, if such were even available, a small red-white bipolar LED for the upper. In addition to the physical space constraints is the observation that LED's don't simulate Mars function as well as incandescents. Accordingly, for me, some compromise with true fidelity to prototype operation, choosing white or red Mars light, not both, was the better part of valor. For my Athearn Genesis/Lombard Hobbies model, I chose to keep the already installed 1.5v white lights, replacing the Athearn circuit board with a TCS A6X decoder. The result is upper white Mars and lower white constant lights, both of which are on, whenever the "lights are turned on," regardless of direction. For my Stewart models, I chose to use 12 v bulbs (from my parts bin), white lower and red upper, because I liked the more dramatic effect of the red Mars light. The Stewart F-units, I think, look good and run very well, but having been around for awhile, do have some shortcomings cf. some newer models. The most obvious is the lighting. On the dual headlight A-units, a single bulb is used to illuminate both headlights via a single clear plastic "lens."
Below are illustrated, step-by-step installation instructions for modifying the Stewart model for independent control of the two headlights using a Train Control Systems A6X decoder. Modification of Stewart (Bowser) dual headight F A unit for independent control of the two headlights using a Train Control Systems A6X decoder: 1. Remove front coupler. 2. Remove shell from chassis. 3. Remove clear plastic headlight "lens" part from shell. 4. Replace shell on chassis. 5. Using a drill bit that just fits into the lower headlight opening (#30, I believe), mark the centerpoint of the headlight opening on the plastic front coupler holder. 6. Remove the shell again, then remove the front coupler holder, then replace the shell. As in the preceding step, mark the centerpoint of the lower headlight opening on the metal chassis, then again remove the shell. 7. Disconnect the left and right, front and rear track power pick-up wires and the red and black motor wires from the clip-in plugs on the Stewart circuit board. Then remove the circuit board. 8. Using a screwdriver, pop off the cover of the front truck gear case, disconnect the drive shaft, and let the truck drop out. 9. Using a center punch, deepen the mark made on the chassis nose. 10. Using a drill press, drill a small hole at that mark. Replace the shell to check that the drilled hole lines up exactly behind the lower headlight opening. 11. Again using a drill press, drill a hole of sufficient diameter to accommodate a metal housing for the lower headlight bulb. (I used a spare diecast metal part, the lamp holder from a Bachmann 44 tonner, but a brass tube should work as well for a lamp holder/heat sink.)
12. Using a pin vise and rat tail file, make a similar opening in the front coupler holder, and replace it in the chassis. Again, replace shell to ascertain that everything lines up correctly, then remove it. 13. Put lamp holder tube in place, checking to see that it does not protrude too far to seat the shell on the chassis. Depending on the diameter of the tube, it might be necessary to file the corners of the vertical slot on the nose of the chassis just a bit to permit the tube to be oriented perfectly horizontally (see photos 1 and 2). Then cement the tube in place with ACC. Photo 1
Photo 2 14. Placement of the upper light is easier, Use the cutout at the top of the coupler holder to hold the tube for the top lamp. 15. Replace the front truck, drive shaft, and gear box cover. 16. Orient the A6X on the chassis. I arbitrarily chose to use the rear light (yellow wire) connection on the A6X board to control the (lower) headlight, and the forward light (white wire) connection to control the (upper) Mars light. (It's not critical, either light is programmable.) However, for a cleaner installation, one should orient the A6X such that leads from the lower light go to the connections closer to the front of the locomotive and those from the upper light can then go untangled on top of the board to the rear (see photo 3). I chose to use 12 v incandescent lamps, so the wires go to the two center connections on either end of the board. With my using the forward light connections to control the upper headlight, I oriented the A6X "backwards," i.e., with the forward light connections on the board facing the rear of the locomotive. If you choose to use 1.5 v incandescents or LED's, the lighting wiring will be different; just follow the TCS wiring diagram.
Photo 3 17. Solder in the front and rear track power pick-up wires, the red and black motor wires, and the lamp wires following the TCS wiring diagram. 18. Test the installation on the test track. If satisfied, clip off the off-center front pin on the plastic motor mount, cover the motor with a piece of twosided foam tape, and press the A6X in place. 19. Painting the inside of the nose of the shell and the inside of the headlight openings black will eliminate "plastic glow through" artefact. 20. Cut the Stewart clear plastic headlight "lens" to make two separate lens assemblies, trimming the lower one so that it fits virtually flush with the inside of the shell, or install appropriate glass lenses. 21. Replace the shell and test. 22. If satisfied, replace the front coupler, and the mechanical work is done. 23. I programmed the upper light (with red lamp) to simulate a Mars light and to be on in either direction of running. I programmed the lower to be constant white. The effect is shown in photo 4.
Photo 4