switch direction lights

Hello All...I am running DCS with an AIU controlling my Lionel O22 switches.  I have a ceiling layout, so it is impossible to see the actual switch when activated.

My goal is to add a green and red light to let me know which way the switch is activated.  Any light will do, whether a Lionel block 153 or a homemade led light.

My switches are wired to a separate power source using the Fixed Voltage Plug on the o22 switch.

I tried wiring a block signal 153 but the red light goes on when the switch is thrown, but immediately goes off.  Same with the green light.

Is there any wiring scheme that would allow the lights to stay lit depending on the switch direction, or is this just because I am using the fixed voltage plug and its momentary only when switch is activated?

Thanks for any help!

San Diego Frank

Original Post

Unless it's in the aui, not wiring alone. 

I think you'd have to do it with relays. The power to throw the points could activate a corresponding relay too. Latching relays hold position till the next signal. One relay activated will drop a power leg off the second, so only one can be active at a time.)

"Still trying to not shoot my eye out"


"Nursing insomnia one railcar at a time"

My aroma therapy? Smoke Pellets.


San Diego Frank posted:


I tried wiring a block signal 153 but the red light goes on when the switch is thrown, but immediately goes off.  Same with the green light.


It sounds like the red or green light turns ON for exactly 1/2 second when the AIU momentarily drives the turnout coil.  In other words backwards behavior.  The red or green light should turn OFF for exactly 1/2 second when the AIU momentarily drives the turnout coil.

Is the common wire of the block signal connected to the "IN" terminal of the AIU Switch port?

Same issue if rolling your own LED indicators; the common wire for the red and green LEDs should connect to the "IN" terminal of the AIU Switch port.  One LED will always be ON and will momentarily turn OFF for exactly 1/2 second when the AIU fires the turnout coil to change to the other LED.


You could wire DZ1000 pushbutton controllers in parallel with the AIU SW terminals controlling your Lionel O22 switch tracks.

When the switch track is activated, the red and green LEDs on the pushbuttons will change with the switch track's orientation.



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Stan/All, I included two photos to show how my AIU is wired to O22 switches.  None of my switches have any wires from their center posts connected to anything else.  Only the outside posts on the switch are connected to the AIU.

Is this where my problem lies? or does this wiring scheme look OK?

Thanks, Frank


Photos (2)


I was suggesting that the COMMON (center terminal) wire from your block signal should go to the AIU SW "IN" terminal for the turnout...which, in your case, is also the "U" terminal of the transformer.  So whichever is more convenient.

As soon as you make this connection, I believe one of the two block lights will turn on.  Then when you fire the turnout via the AIU, that light will extinguish for exactly 1/2 second and the other light will turn on as the turnout changes position.  Again, one lamp (red or green) should always be on.  What you were describing was the backward case where both lights were always off and one would momentarily turn on when the turnout is fired.


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Stan, the wire you asked about is connected from the center post of the 153 to the center post of the O22 switch.

I disconnected it at the switch side and ran a wire connected to it to the Black wire coming out of the AIU like you said....

It WORKS PERFECTLY!  Green light when curved, and red light when straight.

WOW! I can't tell you how sweet this is....to ask a question from a stranger and get this immediate response and sharing of information.



Stan, I had another thought!

I have 6 switches that I would like to have red/green lights attached to.  Rather than go out and look for 5 more 153 block signals, I thought I could build some block signals similar to the 153 using LED's.  I have done this before using balsa wood and drilling holes for the LED's.  That forms the head of the signal. I used some hollow metal tubes as the vertical support.  It actually looks pretty good!

The LED's have 2 legs coming off them and the one's I have used in the past have a rectifier built in to one leg.

Would it be possible for you to draw up a diagram where these wires should go using the O22 switch terminals and the black wire coming out of the AIU ?



"We have already added the Bridge rectifier, the correct capacitor, and the resistor. You just connect to your track power!"

"You will notice both leads on these LEDs are black. That is because the polarity does not matter. The bridge rectifier takes care of this. Connect "either way" you are covered."

Stan, I took the above directly from the modeltrainsoftware.com website where I get the LED's

Thought it might help with the wiring issues.



Connect one black wire from the Green LED to one black wire of the Red LED.  This becomes your "common" just like the center terminal of your 153 signal.  Then connect the 3 wires as you did with the lamp signal.

My only concern is the website says the LEDs operate up to 19V.  From what I can tell you are supplying the turnouts and signal heads with 20V?  Can you lower the 20V or is this a fixed output?

While my guess is you'd probably be OK operating at 20V, it takes about 10 cents of components to lower the 20V to just under 19V just to be safe.  I can draw that up if need be.


Photos (1)

Stan, the power to the switches is from a KW transformer, using U terminal and 20V terminal.  Actual voltage measured is 18.9 volts no matter how I adjust the handle on the KW.

What do you think?  

The wiring diagram is great, and understandable, even to me who has just enough knowledge to be dangerous!!

I will start ordering the LED's and build the structures....I will send a photo when its done..



On eBay you can get 10 diodes for $1.56 with free shipping from a US seller so I'd think you'd have them in a few days.  

1n4001 us seller

Or, you can get them 100 for $1 with free shipping from Asia if you can wait a couple weeks or so. 

Anyway, take 4 diodes and connect them as shown.  This drops the AC voltage by about 1.5V.  So whether it's 18.9V as you measured or the actual nominal 20V, this simple circuit will drop it to below 19V.  Each diode has a silver band on one end.  The orientation is important.

voltage dropper for 20V KW fixed output

For each 3-wire red-green LED pair, the upper and lower wires go to the AIU SW "1" and "2" terminals as before.  But now the 6 center/common wires are tied together and go to the diode-dropper before connecting to the KW "U" (or AIU "IN").  All other turnout wiring is as before.  This configuration can handle more (or less) than 6 turnouts should your needs change.  

If you don't do eBay these are readily available components - something you'd find at Radio Shack if you can find one!


Photos (2)

You can get ten of the 1N4003 from Digikey for $1.37.  Of course, there's about $3 shipping, but if you combine other parts on an order, shipping isn't much of an issue.  You get quality parts for a very competitive price.

Stan, Gunrunner/ All,

Thanks for the info on the diodes. I already ordered some from Evan Designs that are pre- made up. I have used these before and yes.....they cost more, but they have been running ok for years on my layout.  I will keep the other website info on hand for the next project.

Meanwhile, I have started making my 6 block signals.  I have a load of balsa wood and it was real easy to get something reasonable looking.  I have them primed now and will paint them silver with black where the diodes will be.

Stan, I am now going to extend the Black wire coming out of AIU to a centrally located terminal block on the ceiling layout.  I will then run 6 separate wires from the switches to this terminal block.


Stan, OK I get it now!  I think I will try it at 18.9 Volts and see what happens.  Here is another scenario....

I am using the U terminal and the D terminal on the KW transformer to get 18.9 Volts to the switches.

The U terminal and the C terminal give me 6.3Volts.

The C terminal and the D terminal give me 12.2Volts

Would the 12.2 volt setting be better to preserve the LED's?

If yes....Where would I put the old wires that were on the U terminal?  On the C or the D? or doesn't it matter?

Also, would the 12.2 volts be enough to effectively throw the switches completely?

I know thats a lot of questions, sorry, but my electrical knowledge is limited, but I am trying to learn!

The block signals are coming along great...got them painted, now waiting for the Led's to arrive, then drill holes and hook up to new electrical schematic.

Tomorrow, I will run the extra wire through the walls and up to the ceiling to reach the switches. Then a terminal block to send the juice to the 6 switches.

Thanks for all the support....I couldn't do it without you!!!



The KW manual clearly states you need to use the "U" terminal with O22 switches as it shares the same "ground" (outside rail)as the track.  So while the voltage between other terminal pairs would indeed provide lower voltage(s), this cannot be done in the context of the KW also providing track voltage to run engines.

Separately, your LED specifications say they operate between 7-19V AC.  I did not see anything in the description about "constant brightness" so I'm assuming the brightness varies with voltage.  That being said, operating at 12V would consume less power and hence the components would operate cooler which helps to a long and productive life.  To experiment, you could simply connect the two black wires of the LED across the track and adjust the voltage to see if a lower operating voltage might be better in terms of brightness.

I do not have an O22 switch or KW and I find it a bit curious the manual makes a point that U-D pair (20V) be used.  That is, this is more voltage than I'm used to for switch machines.  But I'm not familiar with the history. 


Photos (1)

Stan, thanks for the KW manual info.  I am NOT using the KW for track power.  The TIU is providing the constant voltage, and each track has its own MTH Z 500 brick.  The KW is SOLELY for the switch and accessory power.  Another thing occurred to me is that the KW should be able to adjust the voltage using U and D.  Thats how we used to control trains in the past....move the handle to adjust voltage!  Something is wrong with my KW.  It either is busted or needs cleaning.  I have a spare one and will try it today to see if the handles actually  adjust the voltage.

As manual page above shows, you get adjustable 6-20V under handle control between U-A or U-B.  So it could be as simple as moving the wire from D to either A or B.  Then adjust voltage to provide enough to fire the switch coils which will I'd think would be less than 19V.  Then you're good to go with the LEDs and no diode-dropping required!

Stan, one more time!  Thanks for your patience with a rookie!

The KW is fine...I switched the wires from U/D to U/B The B terminal gives me voltage control from the KW handle labeled B.  (The other handle is labeled A and works in conjunction with the other U terminal to control another train, (which I am not using since the TIU and the brick supply track power.)  So... now....I adjusted the B handle to give 16-17 volts to the switches.  Anything lower and it didn't seem like a really nice positive switch.  Hopefully, this will preserve the LED's I am working on to get the signal lights correct when the switch is thrown.

Evan Designs has shipped the LED's and I will add them to the block signals I made and hopefully this issue will be done and solved...ONLY WITH your help and guidance.  I will buy the next round if we ever meet...who knows! Oregon and San Diego are not that far away.  My wife and I have a camper van (19ft), and we have been all over western and central Oregon.


The diode reduction could still be useful as a failsafe against an accidental bump on the KWs throttle or a small voltage rise in the household ac once the neighborhood shuts off the summer air conditioning. (Mine rises and falls seasonally 18.5-19.9v)

"Still trying to not shoot my eye out"


"Nursing insomnia one railcar at a time"

My aroma therapy? Smoke Pellets.


Stan/ Adriatic/Gunrunner/ All...

Finally got the block signals done.  They came out OK..not fabulous but OK...If I do it again I will use regular wood rather than balsa.  The reason being that regular wood can be sanded very fine and the paint job looks really good.  The graininess of the balsa gives a rough look.  Its not bad with a ceiling layout as the distance you view it at is a bit farther away than a table layout.

The wiring was right on as per Stans expert advise.  The lights switch back and forth from red to green depending on the switch direction.  It is so much easier to tell where the switch is when viewing from below.

The LED wiring is routed through a plastic coffee stirrer from Starbucks!  Just the right diameter to fit the wires and the rectifier package.  The LED and the straw is glued to the wood.

I had some extra bearings left from an old project and used them as bases for the signals.

Also used some finish washers to surround the LED's.  They, also, were glued on.

The top of the signals are some bulletin board pins I had.

Stan...thanks again...you made the job easy...



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