The yellow wire could certainly be used to run ditch lights instead of a rear headlight.
TCS Programming Guide
Remap CV34 to 4. This turns the yellow wire on with F1.
Set CV50 to 0 if you want the ditch lights to be directional, or 32 if you want them to be on regardless of direction of travel.
If using a TCS T1, you could unplug it and plug in a T4X, giving 4 functions. Could put the rear headlight back in, and add rear ditch lights if so moved. At my usual supplier (Hiawatha Hobbies), they are the same price.
Generally, ditch lights are on in the direction of travel. Much easier to see at night with ditch lights. They are required when running over 20 mph over public grade crossings.
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com
When using LEDs, just remember the blue wire on the decoder is the POSITIVE wire. The resistor can go on either side of the LED.
Blue--LED Anode-LED Cathode---resistor----function lead is the same as
Blue---resistor---LED Anode-LED Cathode---function lead
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
If I understand your question, you do not want them to alternately flash? Then yes you can use a two function decoder for this. Just wire them with the appropriate resistors on each lamp and connect one lead to the blue wire and the other with the yellow. If they are bulbs, the leads with resistors won't matter, if LEDs then it will.
Hope this helps.
Will
This is quite possibly the first time I've posted here, but I am curious as to adding ditch lights while using a 2 function decoder. Here is my situation-
I recently purchased a pair of GP15-1s, which would always be running in tandem on my friends layout. My friend offered to supply decoders and paint, and I the locomotives and time. Each of us would get the pair 6 months out of the year. I would like to have operating ditch lights on the units for use at shows and my home layout which is set in the present. I am not concerned with them being solid, non alternating ditch lights, merely being able to light them when approaching a crossing, by pressing Function 1. The TCS Decoders do support function remapping, and since the units will always be permanently MUed, would it be possible to remap the yellow wire (Rear Headlight) to activate when F1 is pressed. Each unit would have them on their forward pilot, and the set would be operating bi-directionally under normal circumstances.
Thanks,
Alex