What's the trick to getting postwar horns working properly?

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  • Member since
    January 2019
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What's the trick to getting postwar horns working properly?
Posted by panzerpete75 on Tuesday, November 23, 2021 4:58 PM

Hello all,

I have two postwar locomotives with horns, a 2353 Santa Fe F3 A-A pair, and a 2338 Milwaukee Road GP7, powered by a refurbished KW. The issue I have, is that the horns only activate on the first "button press" on the whistle lever, and not on the second one which gives a few extra volts to keep the train speed up. The horn relay still appears to be closed when this happens, but I would need to take the body off again to comfirm that.

The selection of whistle tenders that I have all (mostly) work as they are supposed to, where they activate in both positions of the whistle levers. I'm kinda stumped on this, and would appreciate any help. Thanks!

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    February 2014
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Posted by Leverettrailfan on Tuesday, November 23, 2021 10:01 PM

I remember having some issues with those whistle levers, where something was more interested in cooperating when the lever was moved part way, but get it all the way over and not as much luck. I believe that I read somewhere, that initial part of the movement starts with more voltage than when the handle reaches the end of its travel. I think the idea was that the motor in a whistle tender draws more current when it first starts spinning, and doesn't need quite as much extra power once it's up to speed. It probably can't hurt to go over the relays, and to clean contacts in the transformer. I haven't gotten around to troubleshooting my issues yet, so I can’t really offer more advice. I hope to see more input from others, but I am inclined to think it has more to do with the transformer than the trains.

"Unless bought from a known and trusted dealer who can vouch otherwise, assume every train for sale requires servicing before use"

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Posted by emdmike on Sunday, November 28, 2021 12:42 PM

Your only passing 1.5v thru the relay contacts on the horn vs full track voltage on the whistle tenders.  So any amount of pitting or dirt on those contacts can make the horn not sound.  Same for a horn that is internally sticking a bit from age.  I would start by taking the top off the diesel and clean/polish the contacts on the relay.  Then run the engine without the top and see if the horn is more reliable.  if it doesnt still sound on the second push, and the relay is closed, try rapping on the horn body with a handle of a screw driver, see if the horn is the actual issue.   Good luck and post up your results.    Mike

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Posted by lionelsoni on Sunday, November 28, 2021 5:28 PM

The least-destructive way I know to clean contacts is with a fresh dollar (or your favorite denomination) bill.  Slide the bill back and forth between the contacts while holding them closed.

If the horn sounds under any circumstances, it is probably okay.  Check it by closing the relay by hand, or simply hold the locomotive upside-down.


Bob Nelson

  • Member since
    July 2021
  • 14 posts
Posted by trainlivebob on Monday, November 29, 2021 5:58 PM

If you find the relay is working, then you need to test the horn or the wiring from the relay to the horn.  The horn must also have good ground.

After I establish the relay is working, and still dont get sound, I wire the D battery directly to the horn.   If you dont get a sound, then the horn is bad or frozen.  I next put a 9V battery to the horn, but only a few seconds. Two or 3 times.  You dont want to burn it out.  I have successfully loosen horns this way.  Others are just broken up inside when I take them apart, which is my third step (look under the hood).

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