I wanted no-flicker lighting in my Lionel Aluminum Congressional cars. After looking for a way- I happened upon "Dr. Bob's" kits- he sells a variety of kits that are marketed (mostly) for the smaller scales- N, HO, and (some) O. I bought the S/O constant lighting kit. Not being an electronic guru- and since Radio Shack is no longer available to me- buying such a kit was better for me. I was sold fully after I saw what the kits included. In the envelope, each kit includes great instructions, plus everything you need except solder and some way of mounting the battery (I used velcro).
The kits include 3 LED's (plus one extra in case you blow one), the correct resistor, the on/off slide switch, the 9V battery connector, wire, shrink tubing and some tape for the lighting strip (that you make from scrap polystyrene). AND- at only $ 4.50 plus shipping (mail), are the most cost-effective way I have seen to do constant lighting on 3-rail trains. The 9V battery will operate for (he says) 70 hours of running (or three days if you forget to turn it off).
I installed them, and they work great. A couple of tips- the setup is specifically designed for 9V DC battery power, and for the three LED's included. I tried to add a 4th LED- and it wouldn't light. After trying everything I could think of- I wrote an e-Mail to Dr. Bob, and he told me the system was designed for the 9V, and the 9V would not support the 4th LED.
So- his customer support is also terrific. And I am glad I used velcro to attach the battery- so, after 70 hours running, I just remove one end, change the battery, and put it back together.
https://www.ebay.com/itm/O-Sca...6:g:rsoAAOSwWfda13BG
His "Model Train Sounds" Website: modeltrainsounds.com
Highly recommended!!