[CTValleyRR]

Plug and play depends more on the locomotive than the decoder. You can purchase just about any type of decoder with pre-installed pin connectors these days, and provided the loco is equipped with the right kind of socket (8 or 21 pins), they do plug right in. However, in order to get the lighting control you desire, you still may need to do some rewiring and soldering.

As MichaelE suggested, carefully review the documentation that came with the decoders. This may allow you, by changing some settings, to individually control the lighting. If not, purchasing a higher level decoder may be one solution.

One of the beauties of DCC is that you CAN leave your locomotives parked anywhere you please, without worrying about electrical isolation. Sure you can do it if you want, but why bother? The only reason I could think of is that you're drawing too many amps for your system, and there are better solutions for that (power boosters).

As far as the firebox goes, remember that heating that big boiler full of water to operating pressure takes a long time (unlike a diesel, which is warmed up and ready to go in a few minutes). On the Valley Railroad, our firemen report on and start firing a full 24 hours before the loco goes into service. If the loco will be used again within 72 hours, we almost always keep the fire up (it takes far less fuel to keep hot than to warm it again, especially if you're not pulling steam out). Locos really only go "cold iron" when they're headed for an extended period of maintenance (we dump the fire, then either use residual steam to move it to the engine shop, or move it with a switcher). So that light being on all the time isn't really unrealistic.

 

[CTValleyRR]

I have the same ALCO PA as you do, although unfortunately, it's a New Haven livery model, and therefore has neither the second headlight nor the Mars light. I'm guessing you have a different livery, and therefore different detailing. I also have a TCS DP2X decoder installed, although mine does not have the "-UK" suffix. Is it possible you purchased a board designed for UK use, which may have different functionality and / or voltages than the US one -- specifically without Mars light functionality (my DP2X instructions specifically say that the Mars light is separately adjustable; does yours)? Or are you in the UK?

I noticed 2 other potential issues. One is that, on the back page of the Loco manual, under instructions for DCC conversion, the first step is to replace the bulbs with ones rated for higher voltage. So you may have burned out the bulbs. You may want to test on DC again and see if they all still work. Secondly, the pads on the left side of the main circuit board, labeled WBR, typically indicate the wiring colors White, Blue, and Red. I notice that yours don't appear to be connected like that, which may also be causing the trouble.

Good luck.

 

[CTValleyRR]

I think your rewiring may have simply bypassed the circuit for controlling the Mars light, but whatever works.

The decoder paperwork has a lot of options for configuring the Mars light, and I still think your answer may lie there, but as I don't have the Mars light on my loco, I can't actually see if it works...

And FWIW, electricity is not my strong suit. Maybe someone else can weigh in on it?

 

[CTValleyRR]

No, a decoder with wires wouldn't be any different. The pins just substitute for the ends of the wires, is all. I guess you could put the wires to connections they weren't intended for, if you wanted, but I'm not sure what that would buy you.

Here's the thing, though. If it works properly in DC, then there's nothing wrong with the motherboard (and since a P2K is one of the best brands out there, I'm not inclined to fault the mobo.

So you have a couple of possibilities:
1) Defective loco. Not likely, if it works in DC.
2) Defective decoder. Always a possibility; it happens.
3) Decoder with insufficient features to do what you want. Again, unlikely -- that decoder is widely recommended for the loco.
4) Decoder not programmed correctly. You can try resetting to factory defaults (CV8=8) and trying again

 

[CTValleyRR]

The pin arrangement tells you what input / output on the decoder that is tied to. If you were not using a plug and play install, you would have to solder wires (of the colors shown) to various places in the loco to get everything to work properly. Since this decoder has pins, and the mobo has a plug, that's already been done for you at the factory. Assuming the board is not defective.

On the DD side, there is no logic in the mobo; it's just a way to hold various circuits, etc. F0F and F1 would refer to solder pads / circuits on the mobo, and have nothing to do with the decoder. What they're saying is that on their decoder, pins 3 and 6 are intentionally connected, to allow different lights to function from the same CV. The decoder provides the brains... all the basic connections are on the mobo. To see what's wired to what, you have to trace the circuits.

A "two function" decoder means it controls the motor and lights, as opposed to a single function or "stationary" decoder, which has no motor control. You have to look at the specs of the decoder to see WHAT, exactly, it should be able to do and how fine the control is. It sounds like this one should work; the AutoMars function seems to; you can modify the speed table so that 30% throttle gives you a more appropriate speed.

Rereading TCS's reply to you, it doesn't sound like they actually understood the problem, and they're trying to pin the issue back on Walthers. My loco and DCC chip are 12 years old; it's not like this is a new setup you're trying.

You might try Googling the topic. I Googled "mars light on p2k loco with tcs dp2x decoder" and see several results that look promising (and apparently, a similar problem exists with the equivalent Digitrax decoder).