Mars Lights: How did they really function?

Jonathan, perhaps this info might be useful.

Red Mars or Gyra lights on locomotives were used to indicate the train was stopped in an emergency.  This could be activated manually by the engineer or automatically by emergency brake application (loss of train line air pressure).  Opposing movements on adjacent tracks were required to stop if the red was displayed.

The GN (and several other roads) also deployed red Mars lights on the rear of passenger trains. This could be a portable unit, or a permanent one in observation cars, business cars, or "rider" baggage cars normally at the end of a train.  These lights were activated when the train was moving slowly or was stopped (by sensing the output of the axle generators) but it was not unusual for them to be on continuously, either by intention of the crew or failure of the speed sensing logic.

GG1, we have one at the Club, off a C&O Passenger "E" Unit, and it did/does the figure 8, when you turn it on. Voltage is strange though, said that it was 34-70 volts/train voltage? 

I just wonder why the differences? Maybe a DC thing or something!...........Brandy!

One key thing to remember: 

The Mars Signal Light Co. patented the flat figure 8 mechanism that essentially had twin motors, one for the "up-and down" motion and one for the "side-to-side" motion.

The Pyle National "Gyra-Light" could not copy/duplicate the Mars patented flat figure 8 pattern, so their produce produced a different light pattern. 

There is a Model Railroader article from March 1975 that had an article on building a working Mars light. It had a mechanical drive eccentric to give the light wobble kinda like the original.

Just another piece of useless information off the top of my head 

Check out this You-Tube video of a Mars model 888:

https://www.youtube.com/watch?v=6957o6RzdbY

And this original:

https://www.youtube.com/watch?v=JpGQYnI2AhE

Thanks for all the information.  Very interesting.  Glad I asked!

Brandy - interesting on the voltage.  That's a large range for DC power since DC is pretty much a constant voltage.  You have me curious.  34/70 volts is easy to get off an AC circuit using two lead wires and a neutral.  I wonder if the design was capable of multiple DC voltages for use by various manufacturers.  As I recall the Baldwin AS616 at the local museum uses 64V batteries if that means anything. 

I'm sure someone on here knows the answer to that.

The Mars Signal Light dates all the way back to the early 1940s. The available DC voltages would have been 12Vdc, 32Vdc, and/or 64Vdc as used on diesel units. The Southern Pacific GS-4 class 4-8-4s were delivered in 1940/1941 time frame and all had the Mars 12Vdc oscillating head light (not red function). Neither steam locomotive Pyle National Dynamotors, nor diesel electric locomotives, had voltages available other than 12Vdc, 32Vdc, or 64Vdc/74Vdc for charging. In fact, Diesel units had/have 32Vdc headlight bulbs and had a large voltage dropping resistor to maintain that 32Vdc. 

The Model 888 was for emergency highway vehicles and does a double horizontal figure-8 instead of a single, as was used on locomotives.  However, I did operate a UPRR/D&RGW Sunnyside coal train (Santa Fe handled them from Barstow to Kaiser) with a Rio Grande SD45 on the point, and its Mars light did the double figure-8.  I presumed that the shop had repaired the gearbox and put the wrong gear in, but possibly it was intentional.  This was the only double figure-8 I ever saw on any locomotive, including the other Rio Grande SD45's.

The second video demonstrated the typical railroad pattern.  Some railroads increased the oscillation speed while others used the one demonstrated.

There was a gear box behind the headlight housing.  One crank and rod was on the top of the gearbox, while the other was on the side.  They were synchronized so that the oscillation formed a figure-8 pattern.  The last Santa Fe engine I ran with a genuine Mars light was rednose dual-service unit 328L in 1970 or '71.

One additional - and unusual - use of the red oscillating headlight was exclusive to Santa Fe.  In Automatic Block Signal territory, on single track, if a train stopped at a block signal displaying Stop and Proceed (a red aspect or horizontal semaphore blade, with a number plate mounted on the signal mast), the train, after waiting 5 minutes, could proceed at restricted speed to the next signal.  Engines equipped with a red oscillating headlight were to display the red light throughout the block.  This was to make certain that any engine or train at a switch within that block, which might have been considering entering the Main Track, could clearly determine that the engine whose headlight was visible was advancing, and not waiting at the signal.