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1966 C10 Horn Ground #1328172 Sun Sep 29 2019 11:27 PM
Joined: Jul 2009
Posts: 65
T
Tim-o Offline OP
Wrench Fetcher
I’m putting the truck back together after changing the directional harness and getting that whole thing back to working. I put on a new horn relay and tested the connection to the horn by creating a ground to the non horn connected ground tab on the relay. Horn works. I put the steering wheel back on with the spring loaded contact installed and touching the brass ring on the directional harness. By creating a ground, and touching the spring loaded button the horn works. That tells me the connection between the steering column and the horn relay is good, the horn relay is good, and the horn works. So my question is...

Where does the ground come from for the horn? I have a spring disk from LMC and the three screw isolator and a metal cup that the isolator attaches to. The spring disk was not there when I removed the steering wheel but that doesn’t surprise me because the previous owner did lots of crazy things - and it had an aftermarket steering wheel when I bought it.

Does the steering column when the steering wheel is fully attached create the ground? I haven’t put it completely back together yet and tried it.

Tim-o

Re: 1966 C10 Horn Ground [Re: Tim-o] #1328218 Mon Sep 30 2019 11:02 AM
Joined: May 2005
Posts: 6,378
B
bartamos Offline
Master Gabster
1. Where does the ground come from for the horn?
2. Does the steering column when the steering wheel is fully attached create the ground?

The horn wire, up thru the column, is a ground wire to a slip ring on top of the mast bearing. This wire, as you know, comes from the relay's ground terminal. The horn trumpet's terminal is wired to the relay's output terminal. 12V power is attached to relay input.

The horn body is grounded by it's attachment to the body. Column is grounded by it's attachment to body. When horn button grounds the disc, you are, in turn, grounding the plunger contact under disc, which rides on that slip ring on the mast bearing. This grounds the relay trigger. The relay's electromagnet pulls an armature that closed the contacts inside relay, which connects the relay's 12V input to the relay's 12V output to horn, which trips the diaphragm contacts inside the horn and the diaphragm vibrates (honks).



I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: 1966 C10 Horn Ground [Re: Tim-o] #1328418 Tue Oct 01 2019 07:00 PM
Joined: Jul 2009
Posts: 65
T
Tim-o Offline OP
Wrench Fetcher
Thank you Bartamos for your detailed explanation of how the horn system works. You were, of course, correct. What threw me a curve was, in the horn cap container parts kit I purchased from LMC (part number 34-0411) , the spring disk that is installed first had not only the three holes in it for the spacer to bolt through, but also had two smaller holes drilled on either side of the three holes for the spacer (take a look on the LMC website). The spring loaded push button that contacts the brass ring on the wiring harness almost lined up with the smaller holes in the spring disk. All of the other spring disks I have seen have only the three holes and three slots to provide the spring disk flexibility (I presume). Anyway, once I had everything properly in place and tightened the steering wheel nut down, and put the cap on, the horn worked. I do appreciate all who read this post and thanks once again for you answer Bartamos.

Re: 1966 C10 Horn Ground [Re: Tim-o] #1328430 Tue Oct 01 2019 08:57 PM
Joined: May 2005
Posts: 6,378
B
bartamos Offline
Master Gabster
I agree, the only disc I've had are the slotted kind. Possibly there was a design change. It may be cheaper to make without slots....or it may perform better.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: 1966 C10 Horn Ground [Re: Tim-o] #1328446 Tue Oct 01 2019 11:50 PM
Joined: Jul 2009
Posts: 65
T
Tim-o Offline OP
Wrench Fetcher
This had the slots... and additional holes..

Re: 1966 C10 Horn Ground [Re: Tim-o] #1328466 Wed Oct 02 2019 12:56 AM
Joined: May 2005
Posts: 6,378
B
bartamos Offline
Master Gabster
OK, I'm confused. Looked at LMC part number you gave and picture of disc shows no slots. I thought that is why you gave part number. It's OK, no big deal.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.



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