Wouter and Dave are correct.? My preference is to put a resistor (one per LED) in the blue wire.? The reason I do this is that it provides better protection for the decoder power supply in the event of a short circuit in the light wiring.? If the resistor is in the function lead a short circuit in the light wiring could cause the decoder output on the blue wire to fail (let the magic smoke out).
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Dale Gloer
Layout Supervisor, Southern Alberta Model Railway Club
Dale Gloer