Hi, Jack from Star, Idaho.  Awhile back I submitted a blog for non.flickering lights.  Here is the solution that worked great!  I used a device called a "constant voltage source."  The item is a LM334Z three leg device that is tiny and will fit into any car or engine easily.  I purchase it from "Electronic goldmine" for a cost of $.79 each.  I found this can work from 12-20 volts and control lights or a sound only decoder.   I have not tried it yet with sound and motor control however, it should work. 

Any way here is a web address that shows how it is hooked up.  If you use it for a decoder you do not need a resister, just connect two of the three leads together and no more break-up of sound from momentary power loss.  Go to http://www.pollensoftware.com/railroad/circuit.html  hit the link on the left "wiring diagram" and you will find a simple to follow diagram illustrated for simplicity.  If the link does not work just type in the address.  Once you are on the site you can follow various links that are usefull for. The device needs the proper resistor if you are using it with an LED.  I have hooked this up in all my dummy engines for the sound only decoders and I no longer have a break in the sound when the electrical pick-ups loose contact with track voltage.  The same is true with car lighting.  The circuit is simple, inexpensive, an easy to make with very little soldering skill.  Other sites such as "Train Aids" has a wide variety of products at really cheap prices!  check it out and I think you will be please with results.  No more expensive car lighting systems...

Glad to share a good thing with fellow railroaders

Jack Strong