How to wire lights to decoder motor wires?

[john_ibw]

I was told another thread already exists that shows how to connect lights to motor wires of the decoder. But, I can’t seem to locate it.

I am using the Digitrax DZ123 for the cab cars. The directional lighting will make use of the available functions. I was considering wiring the lights to the decoder wires available for the motor. Question is, do I need a resistor in series? If so, which one? If someone can direct me to the earlier post, that will be much appreciated.

[quinntopia]

Hi John!  Not sure how many different ways there are to do this, but I recently did a conversion on an old Roco locomotive that I wanted to replace the old bulbs with LED's.  Although I used a DZ125 in my install, I think they are basically the same for this part.

All I did was solder a 680 ohm resistor onto both the white and yellow wires coming from the decoder before they get attached (soldered) to the appropriate leads on the LED's.  The blue wire does not need a resistor and would go to the other leads on each of the LED's.  Hope this makes sense.  There's some photos on my blog that might help you as well:
http://quinntopia.blogspot.com/2011/01/locomotive-roster-sncb-series-59-roco.html

There's others on this forum who know a lot more than I do about decoder installs, so they may be able to provides some additional information as well.

Good luck!

[The_Ghan]

John,

I touched on this in my doc to you.  However, to clear things up don't wire any lights to the decoder motor wires.  I headed down this path early on, before properly understanding the decoders.  The DZ123 and DZ125 both have the appropriate wires and functions to automatically reverse the lights.  Wire in accordance with the diagram on page 3.  You should replace the bulbs with LED in the cab cars.  Then wire a 1K Ohm 1/4W 1% carbon film resistor across the motor wires.

Direct email from Digitrax originally instructed me to use a 120 Ohm resistor.  KenS pointed out to me that a lot of current would still go through the decoder and it could fry.  I tested a 1K resistor and reported back to Digitrax.  They concurred that 1K was suitable.  The decoder just needs to identify some current passing through the circuit so that it reports back as being properly wired.

Then set all three decoders to the same address.

Cheers

The_Ghan

[john_ibw]

Understood. Thanks. I got confused at the resistor part earlier. Now I get it. Thanks!