Horn issue on Postwar F3

I have installed a new horn (original, not squeaky reproduction) and it was tested with a 9v battery and it works fine. There’s something in the battery circuit when it’s in the engine that’s causing it to not sound.

this is why these are no longer made.

they were always finicky even when new.

sometimes the relay doesn't release so the horn never shuts-up.

you have the opposite issue.

IT HAS BEEN A WHILE since I ran old engines. As I recall the relay is DC and the engine is running AC; when you press the horn button on either the transformer or separately set up button switch, it temporarily sends a DC pulse to trigger the relay.

Are you sure you're sending a DC pulse?

Alan,

im running a complete postwar layout with a ZW transformer. I’ve never had a problem with the horns or whistles. The relay is closing just fine. I’ve adjusted to tone screw as well. I’ve found a point where it sounds like it wants to blow the horn but it’s just a low rattling or gurgling sound. I guess my question is, does the corrosion present on the battery cover and on the frame interfere with the operation of the horn?

The frame does have corrosion on it from the previous battery leakage. This is the original frame and paint, which is also flaking off in some spots. I actually replaced the battery holder because the original was totally rusted and ruined. That and the relay were shot and I replaced them. I have double checked the wiring a few times, both with diagrams and up against my 2344 wiring. They are exactly the same. There is the insulated strip between the battery holder and the frame as well, and there is a ground connection. It’s strange because everything looks like it wants to work, and the relay closes and opens as it should, both in manual operation (pushed by hand) and with the ZW. I sprayed WD40 onto the rivet holding the battery cover on, at the pivot point, hoping that would eat away some of what’s left. I did lightly sand some of the corrosion off the frame where the battery sits, but none of this works. The jumper wire…from the screw with the washer on top of the bracket to any spot on the frame?

The repair guy, Andy, for our LHS gave us this tip one day.  It worked for the customer standing hopeful at the counter.  It was the holidays.  He couldn't release the beepless engine to our repairman's timetable, so he was looking for that 'quick fix'.  Or he would return after the holidays to have it repaired without urgency.

Anyhow, if the unit has been in horn-hibernation for an extended period of time, Andy suggested it might need a 'rude awakening'.  IOW, remove the horn from the engine (unsolder the positive connection at the relay).  Now attach variable DC leads to the horn frame and wire (2-rail 18v variable DC powerpack, etc.).  Set the rheostat at about its mid-point.  Turn on the power pack for a quick 'jolt'.  You're giving it a shot of more than the 1.5v of the D-cell batt.  If the horn 'awakens',  turn the power off, reduce the voltage a bit, turn the switch on and see if you're still getting the 'beep'.  Dial it down a bit more, repeat.  Then, if you have a multimeter, set the voltage to 1.5v and give it another try.  If she's still beeping, you should be good to go. 

If the voltage when set at the midpoint didn't wake it up, increase the voltage and try it again.  But don't leave the DC power on at the elevated voltages (i.e., >1.5v DC) for more than a couple seconds.  You're just trying to wake it up...not cook it for breakfast, lunch, or dinner!!

Once you get repeatability at 1.5v, then make your adjustments for sensitivity and tone with the adjustment screw/nut on the bottom of the horn.

It worked on the first time for our hopeful customer! (No charge!) But Andy confessed that sometimes the technique just doesn't work.  One can get into the horn by carefully bending back the several crimped fingers holding the horn assembly together.  Just bend them enough (about 90º max.) to be able to release the cover and the horn diaphragm.  Carefully clean the internal contact points, place the diaphragm and cover back into position, but don't re-crimp the fingers just yet.  You can gently clamp the assembly, use some tape to hold it together, etc., but you'll want to apply that 1.5v again to see if your cleaning of the contacts has you on the right track. 

Once you feel the beep is back, then carefully crimp the fingers back. 

Like I said, I don't know whether this is a copacetic technique among the most learned, but it sure worked the one time we tried it.  Talk about a happy customer!...and a couple of enlightened folks behind the counter!

FWIW...

If you're successful in getting the beep back, let us know how you did it!...you know, the rrrrest of the story!

KD

Jim

All of my Postwar is behind glass! I never run them anymore.

So corrosion does inhibit the electrical flow to some extent. It does sound like the horn is not getting enough of the battery to power the horn since it works at 9V.

it's only 1.5 V I don't know what the horn is rated for.

I would double check the electrical continuity from the contacts to the horn.  Then I would use a probe to "inject" the desired voltage along both sides of the horn circuit.

Be sure you replaced the shouldered washers on the battery bracket frames or you will have a direct short with the battery. One trick I use when I get postwar diesels in for repair is get a small length of flexible wire and solder it to the top of the battery contact rivet and the flexible copper tab on the back of the relay armature. This provides a positive path for the battery current. Be sure you have polished the silver contact points that close also.  

Chuck,

the washers you’re talking about go directly under the screws that hold the bracket down, correct? I have them, and the insulation strip as well, in place. When you say the battery bracket rivet, where are you talking about on the bracket? I installed a brand new bracket. I will try the soldered wire trick if I know which two points to solder the wire on. Any chance you have a picture? Also, my other concern is I’m losing the connection on the negative side of the battery from corrosion on the battery cover and surrounding opening on the frame. I polished the inside of the battery cover so the small pointed center of it is clean when it makes contact with the negative side of the D cell, but is it possible that’s where im losing the connection?

A couple of pic's. Take a file and swipe across the top of the battery contact as solder won't stick to the plating. Solder a wire there and the other end to the copper tab on the bottom of the relay armature. Helps a lot. The battery cover screw when tight should provide the ground if the battery door swing rivet is corroded.

I’m definitely going to try that, Chuck. Do I solder the wire to the spring-loaded contact or the bracket itself? And on the relay, the brass tab I assume is the one under the relay plate that moves up/down when activated?

The spring loaded contact.

Well….nothing. Soldered the wire on both spots and I still got nada. I’m at a total loss. I can’t figure out where I’m losing power that the horn won’t sound. I scrubbed off more of the corrosion on the battery cover so it’s pretty clean. The small pointed contacts on the cover are clean now. The screw is clean. Even the rivet looks good now. The only visible corrosion is the opening to the battery. But the frame is grounded, the wiring looks like it’s supposed to, and I’m getting a low gurgling or rattling sound from the horn at one spot when adjusting the tone knob. I’d rather not open the horn and risk breaking the tabs. Done it before with success but this horn was tested and worked before installing it. Totally lost….