Postwar Great Northern horn relay.

Try operation the horn relay on 5 volts of DC.  You could use three batteries in series.  If relay works, try operating the horn using the horn relay. If both of these work, put a DC volt meter on the track and see how many DC volts the transformer is putting out to blow the horn?  Should be be about 5 volts to get it started and more than one volt to hold it in. If the transformer is using the old style disc rectifiers there will have to be some load on the circuit to get the DC to flow.  Usually three passenger cars with incandescent lamps will do it. If all these are good, then problem maybe in getting the DC to the horn relay.  Usual things are clean track, good rollers and springs, no rust or dirt on roller pin, good connections in loco wiring, etc.  What transformer are you using? 

I assume your talking about an EP-5 electric? the horn itself is obviously powered by the battery, you need to determine that the relay is closing the connection between the horn wire and the battery itself. If you want to get technical, you can hook up a volt meter between chassis ground and the horn wire and verify battery voltage is coming across the wire heading to the horn. do this while sitting on the tracks and pushing your whistle/horn button or switch. watch the action of the relay to confirm its sucking up the bottom plate to make a good contact. from what you are describing, sounds like the relay is doing its job. there should be a fine adjustment screw on the horn itself. sometimes a replacement horn needs a little tweeking to get it right. If everything is working as it should, with a battery in the loco, turning the loco upside down in your hand should make the horn sound. On the tracks, with the shell off, while pushing your button watch for odd tiny arcs from all the connections associated to the horn wiring. Including the horn itself. if none of this helps, perhaps post up a video of the engine with the shell off, and everyone on here can give pointers and ideas too......Pat

The relay should pick up at 1.5 volts and hold at .5 volt. Is the hon relay buzzing, or are you hearing the reverse relay (E-unit)? If you tap the cab then it works, I would say a horn adjustment. You said you have a new horn, original or reproduction?

Looks like this fixed it. Take a look at the at the copper tab in the red circle.  It conducts current to the plate on the bottom of the relay and as the relay gets older the tab  looses its tension and in my case will intermittently not pass current to the plate. Bent the tab a little and the relay is working every time now. Thanks for all your help.  Bill Makel

A better repair would be to solder a very flexible wire to the bottom plate and the other end to the solder point on back of relay.  Something like eunit wire would work well...

Marty

let us know how you found the problem.....did you catch it the act?....did you see some arcing? posting up your diagnostics will also help the next guy....hope we all were able to help you

A better repair would be to solder a very flexible wire to the bottom plate and the other end to the solder point on back of relay.  Something like eunit wire would work well...

Sometimes I carefully disassemble the armature plate and clean the contact areas.
Other times I solder a wire between the plate and the back of the relay. I find that using a few strands of bare wire is sufficient.

I try to avoid bending contacts.

Marty has a good idea and if the relay acts up again I will proceed along those lines.  I discovered the fix by eyeballing the route of current flow and realizing the contact at the rear of the relay was not consistently passing current to the point plate. Thanks for your help.  Bill