Post War Switcher Horn Issue

Chances are the issue is with the horn relay and not the horn itself.

 

First off, do you have a battery installed? (not sure how familiar you are with the horns, but on NW2s they require a "C" battery to work.

 

If the battery is installed, the horn should sound if you turn the switcher upside down, otherwise there is a problem.

 

if it doesn't sound when turned upside down, check the relay. It's screwed to the horn assembly. take a small screwdriver or something of that sort and push the contacts on the side of the relay together. If it still doesn't sound, then an issue definitely exists, but it might still be in the relay. The contacts might be dirty, or the relay damaged internally.

 

You can bypass the relay completely. Without looking at the diagram, I believe the process is to run a jumper from the negative on the battery to the horn case, and the single wire coming from the horn to the positive. This I am not certain about, but it is either that, or the reverse. The horn should sound. This would indicate the horn is fine and the relay requires repair/replacement.

 

If that doesn't work, there are replacements on eBay that range from $20-50 depending on whether the relay is included, whether it is repro or old stock, etc.

 

 

Here is a tutorial on diagnosing and repairing postwar diesel horn circuits.

Larry

Often the contacts inside the horn are dirty and need a little help to get going.

Here are a couple of tricks:

 

1 - take a set of test leads, connected to a toy train transformer set to about 10-15 volts AC.  Connect one to the lead coming from the horn. Brush the other against the horn body. Sometimes the jolt of higher AC voltage will get it going. A quick connection will not hurt the horn, but don't run the horn this way for any length of time.

 

2 If the first step doesn't work, then hold the lead against the horn body. Take somethng like a screwdriver and sharply tap the diaphram (inside the sound hole in the horn). This will often get it started.  Again, don't run the horn this way for any length of time.

 

As Andrew wrote above, sometimes the problem is dirty relay contacts, or poor conductivity between the battery and its holder.

Sometimes the relay armature (part that moves) doesn't have good contact with the relay body.

All this can be addressed with careful cleaning. (I have my doubts about how effective just using a contact cleaner would be)

 

Thanks everyone for your help. So far I got the horn to blast with power from the transformer, so going to tackle next steps on the relay this weekend.

 

Thanks,

 

Jim

The issue can be anywhere that electricity is conducted by metal to metal contact in the horn's circuit. It can even be the battery contact on either end.