Horn relay question, D25

[bamfordsgarage]

I've just swapped a replacement steering box into my '47 Dodge D25 (P15). One related task was adding a few inches to the horn wire and a plug in connector between the steering tube and main wiring harness.

 

Now the horn no longer blows when the horn ring is pressed. Logic, and the way things often go in this garage, would suggest I've screwed something up with the horn wire/contact/ring, etc (basically, the last things I "fixed"). But this time, maybe not. The wiring appears to check out and I suspect the relay.

 

Relay photo is attached, and as I understand it:

 

 - top terminals are the switched circuit

 - Bottom terminals are the control circuit

 - Bottom terminals should have continuity through the relay coil (they do not).

 - An audible click should be heard when 6-volts are applied across the bottom terminals (it is not)

 

I have confirmed that the horn wire has continuity from the relay to the horn ring, and does ground when the horn ring is pressed. The horns honk loud when the top terminals are jumped and less loud when the upper left and lower right terminals are jumped.

 

It seems very unlikely that the relay would fail, right now, by chance. So, maybe I've damaged it somehow, or maybe my assumptions are incorrect and the problem lies elsewhere. I endeavoured to get it apart for a look inside, but that composite base is very reluctant to come out of the housing. There's a chance of damage if I force it, and I don't want to go further in that direction until I'm more confident that the relay is faulty.

 

Comments and suggestions most welcome!

 

[Conn47D24]

Sometimes the terminal names are marked on the "tabs" where bolts go thru.

Check that for correct wiring.

 

[Plymouthy Adams]

I can see this relay has been gone into by the lifted tabs.....it is not a hard task to check the relay with a VOM.   As you have the terminals marked, the relay coil should read resistance of the coil that energizes.  If your have the 12 volts switched...the horn ring is as you said going to ground, then either your contacts are dirty or the connection is dropping voltage and pulling strong enough for a good contact of internal connectors.  Do a voltage drop test if needed but I would ensure good clean connections first.  you can disconnect the horn (always hot) and the horns themselves and read these contacts with the volt ohm meter for continuity and then again if this tested good with a voltage drop test...cleaning the contacts internally as it could well be corroded with the cover loose as pictured.  Two circuits, one energizes, one relays (connects internally)  

 

If pinout is suspect...the coil that energizes is one circuit and can be polarity either post.....the relay contacts are the other circuit and also can be polarity either way...as the tabs are lifted a quick visual is all that is needed here.

[JBNeal]

additional information - D25 wiring diagram for horn relay

 

looking at your relay terminal corrosion, this may be an issue driving up impedance, which could also be present internally.  The risk of pulling terminals off while rocking the relay out of its cover is significant.  I have sometimes remedied this by massaging the metal cover to break the base loose enough to insert a dental pick into the corners, then work around the edge to further open up the cover to allow for relay withdrawal.  This is a tedious hands-on procedure that does not always work given the fragile state of the relay internals.  So whenever I see corroded relay terminals,  I assume the internals are just as bad and attempt to source a replacement.

[RobertKB]

Chris, here’s the horn relay in my D25. Also shown is a spare I have. Both show one connector of a little different style. Other pictures show the labelling for each as mentioned above. 
 

 

 

 

Edited February 27, 2021 by RobertKB

[bamfordsgarage]

Thank you all for the comments, photos and suggestions. JB’s link also yielded an easier-to-follow wiring diagram. 
 

The horn is finally sorted, — terminal corrosion was an issue and it took some head scratching to figure out that my newly-installed steering column was not grounding reliably until the pitman arm went on. 

[Tom Skinner]

Not to complicate this post, however, when my horn quit working, I saw I had to replace a relay to make it work again. I never had this, or saw this configuration on my previous Chrysler Royal or my Chrysler Club member's Chryslers (All 1946-1948) Why do I need this relay? It is pictured to the left of my Horn Relay below

[Tom Skinner]

I believe it has an S - B - H designation on it. I tried doing away with it by rerouting wires directly to my horn relay which looks like yours with no luck,

It is a 6 Volt Horn Relay I bought at Carpenters (Ford Supply) for $14.99 so I am not complaining. Why the He double Hockey Sticks do I need it?