I just solved one problem. I just bought a package of Evan Design LED's .
They have a resistor and a Bridge Rectifier already attached. It allows an input voltage of 7 thru 19 Volts. It can used for AC,DC,dcc because of th rectifier. It says you can get the power right from the track. I will let you know how it works.
Because of the resistor they hook up several LEDs in parallel.
Harold