horn blows when steering column grounds with tool - Normal?

[mole2000]

I got my horn wiring sorted out a few weeks ago and it works great from the steering wheel, but was still working on some other items under the hood when my wrench touched the column while tightening a nut on the inner fender. Of course my head was a foot away from the horn. Yikes! It still works well. Is that normal or should I check for a wiring problem?

Thanks.

[Longhorn Man]

wow... that's a new one by me. it shouldn't do that.

[david jobs]

Sounds like the contact under steering wheel is touching the column tube,then when grounded it blew(wrench making a ground from inner fender to column)That would be where I would start

[Longhorn Man]

except, the whole column is a ground... it's bolted to the dash... and connected to the steering gear box... which are both grounds

[VetteVet]

Well I pondered on this one too and the only thing I can see is that the steering column horn wire is grounded to the column. The problem with this is that the horn should blow all the time as is so often the case "unless" the column is not grounded. I am having problems with that since the column support is bolted in. If there is a rubber support insulating the column that would explain it. The wrench grounded the column and the wire in the column completed the circuit to the horn relay and blew the horn.
If the horn was working normally before then the column had to be grounded. It's time to get the meter out and check some continuities.
I'll be watching this one.

[david jobs]

Thats true that the whole column is a ground-but the contacts dont need to be grounded til the horn button is pushed.Im not exactly sure how the horn is wired on a 67-72 but the commecial trks I repair everyday are wired with a constant power to horn assembly and the button connects the ground-so if its wired that way I would say one of the wires or contacts is touching the column tube

[Longhorn Man]

on these, the horn button sends a ground signal to a horn relay, which then sends 12 volts out to the horn which is grounded through the bolt that mounts it.

[david jobs]

So is it possible that ground from button to relay has a bare spot that may be contacting the column?? So when wrench connected it completed to ground circut??

[mole2000]

Thanks for all the replies/discussion. I took the wheel off this morning to see what was going on. Since it's an aftermarket wheel some things are a bit differently structured but I think the principals should be the same.

I had a short within the metal adaptor block where the "middle piece" is and get power at the black wire attached to horn button plate. When I ground it I can hear the relay clicking. But after hooking the wire up and installing the button the horn doesn't work. And it also will not sound when grounding the steering column under the hood... So I'm not really sure where to look now.

I have power at the brass piece that is attached to the main column assembly and when attached the power passes through the metal plunger on the middle piece. Between the middle piece and the black wire was where the short was, I believe. I used some rubber line and electrical shrink tube to insulate within that metal block. So now I think I fixed one problem, but still no horn. This may take some time to sort out.

So when I press the horn button, that closes the circuit which energizes the horn relay, which sends power to the horn. Do I have that much correct?

sorry about the fuzzy picture...

[david jobs]

So the horn worked with the button b4 repairing wire in column? Do you hear the relay clicking with horn button?

[gophersnake]

For whatever help this may be to mole2000's troubleshooting, here's some info taken from the official GMC wiring diagrams for a '68 CM 2500:

The engine compartment diagram shows the horn grounded somewhere very close by, probably through its mounting bolt. It gets its power through a "12DG" (#12, dark green) wire from one of the firewall connectors.

The cab diagram shows another 12DG wire between the firewall connector and the horn relay (which looks like it must be under the dash, not under the hood).

The horn relay gets its power through a 12R (red) wire from a 5-wire junction not far away. The wires at the junction are always hot; they're powered from the fusible link near the battery and carry power to the fuse block, the headlight switch, and the ignition switch.

The horn relay is operated by grounding it through its third wire, a 20B (black). This wire is shown running to the C-shaped, 8-wire "directional signal connector" on or in the steering column. On the other side of the connector an 18B wire (perhaps part of the directional signal harness) runs to the horn contact. The other side of the horn contact is shown grounded somewhere nearby, perhaps to the steering column.

So when I press the horn button, that closes the circuit which energizes the horn relay, which sends power to the horn. Do I have that much correct?

Yes, that's the way it's supposed to work. It sounds as if your steering column may have been (a.) ungrounded and (b.) shorted to the horn relay wire so that when you touched it with the wrench you were in effect grounding the horn relay. That doesn't explain why the horn still worked normally from the button unless there was another ground path for it -- through the steering shaft, maybe.

I'm with VetteVet -- check out all of the above with a meter (or something -- I prefer a test light myself, the kind with the spike at one end and the alligator clip at the other, because it's so much easier than juggling a meter).

[mole2000]

It seemed like what worked before stooped working when I fixed the short, although I recall not checking horn before fixing. I wish I had, but too late.

I will check again this morning but I do not hear the relay click when the button is pressed. The PO had modified the horn button to work around a problem with the wiring. I replaced the standard column with tilt and removed the old wiring and everything worked, until the accidental short under the hood.

I have an aftermarket wheel- could that be non-conductive? I wouldnt think so..

So yes, it appears I'll be tracing down where the mistake is using a test light. Thanks for all the good advice and I'll update with any results.

[mole2000]

I did get this sorted out. I found that the steering shaft was not actually grounded. It seems that the coupler at the steering box was breaking the ground. I ended up creating a short jumper wire to get the ground across the coupling. I dont think that there was any jumper originally. I guess I was overzealous with my parts painting before assembly.

That issue combined with the short in the hub adapter was causing the unexpected horn blowing when the shaft was grounded.

Thanks for the advice.