I just finished installing the LED's in the firebox of an MTH 2-8-0 Rail King with PS-2.
I used two 3MM flashing LED's one red and the other orange. I drilled out the firebox so the two LED's would install side by side. I don't know what method you use to install LED's, I use small pieces of duct tape to hold the LED's and the wires in place. This method is in the event we want to remove them at some future time.
I routed the wires from the firebox to the top and along the inside of the boiler, so as not to interfere with the flywheel and the top board. I used a small plug (2 Prong) which can be unplugged if and when I remove the boiler...soldered the wires on part of the small plug to the smoke unit fan motor, and the other wires of the small plug to the LED's going to the firebox. There is enough room to install these LED's and the wiring and plugs. I fired up the 2-8-0 and using my DCS system, it works great, giving lots of illumination.
Now, if you are using your DCS system to run your locomotives, try this: on the Hand Controller, look for button number "1" labeled Smoke. Push it while the engine is running or sitting. The LED's go off and you can turn them back on again, this does not interfere with the smoke unit or fan, and there is no noticeable break in the flashing of the LED's.
Be sure to stay away from the Tach reader, you will cook the board or burn out the tach reader. They have one purpose and do not need any other wires attached. I do not recommend attaching any wires to the motor leads either.
I like the operation of the LED's in the 2-8-0 and I already have another two to do for customers who were here when we tested it.