If you mean, will it work hooked up the a function output of a decoder? Yes, it will but it is not optimal. We can eliminate the bridge rectifier since the decoder already does that for us. The next thing is that the inrush current (when the capacitor is recharging after a power dropout) might be a bit high for the function output of a decoder. Same goes for the total current consumed by the LEDs. I have to check into that.
The other thing is that the circuit I designed was to smooth out any voltage dropouts caused by poor electric pickup (which seems to be a common problem in passenger cars). But if your car has poor electric pickup then that will cause the decoder to cut out too. The anti-flicker capacitor is on the LED side of the decoder, so it does not keep the decoder working during power dropouts. When the continuity is reestablished, the decoder needs to "reboot" to get back into functioning state. Depending on how long that "reboot" lasts, the flicker-free circuit might not have enough capacitance to keep the lights on.
But if you are willing to try it out, I can redesign the circuit to be hooked up to a decoder's function output.
EDIT: Here is the modified circuit
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As-is the maximum current will be around 70mA (which should be safe for most decoder function output - check the specs for your decoder). The value of R2 can be changed (reduced) to increase the brightness of the LEDs The value of 15 K Ohm was the value which was selected by the person which asked me for the original circuit.
