horn won't work
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Tuned
Joined: Nov 2007
Posts: 308
Likes: 5
horn won't work
I need some help trouble shooting my horn circuit. Not sure exactly where to start, but I have a grant steering wheel so no ford horn strip there.
I hot wired the horn to the battery and it does work. using a test light
I do not have any juice at the horn relay (other than the constant hot) when the horn button is depressed.
What's next?
I hot wired the horn to the battery and it does work. using a test light
I do not have any juice at the horn relay (other than the constant hot) when the horn button is depressed.
What's next?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Can you describe the test you're doing when you say that you "do not have any juice" at the horn relay? I.e, what test are you performing, what results are you expecting, and what are you seeing that contradicts your expectations?
To give you some background information, there is no switched power source that runs to the relay (your post indicates you expect otherwise). Hot-at-all-times power goes to the relay through the YELLOW wire. When the relay closes, that power comes back out through the YELLOW with GREEN stripe wire. To make the relay close, the BLUE with YELLOW stripe wire is grounded by the steering wheel.
If this is a '78 or '79 without cruise control, there won't be a horn relay.
To give you some background information, there is no switched power source that runs to the relay (your post indicates you expect otherwise). Hot-at-all-times power goes to the relay through the YELLOW wire. When the relay closes, that power comes back out through the YELLOW with GREEN stripe wire. To make the relay close, the BLUE with YELLOW stripe wire is grounded by the steering wheel.
If this is a '78 or '79 without cruise control, there won't be a horn relay.
Thread Starter
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Tuned
Joined: Nov 2007
Posts: 308
Likes: 5
This is a '75 F250 4x4 and I was not sure if the relay required a voltage signal to switch the relay or a ground connection so I was checking with a test light to see if the blue wire had any voltage when the horn was depressed, but it sounds like it is part of a ground connection. So this blue wire runs back to the steering column connector and then up to the horn brushes?
No sure if my test leads are long enough to check for continuity between the relay and the steering wheel
No sure if my test leads are long enough to check for continuity between the relay and the steering wheel
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Yep, you got it. The BLUE with YELLOW stripe wire grounds out to turn the horn ON. You might try disconnecting the BLUE with YELLOW stripe wire from the relay and grounding out that terminal to see if the horn comes ON. If it does, you know the problem is the relay ground. If the column isn't grounding, you might need to run a jumper wire across your rag joint. Or, your steering wheel isn't shorting out the brushes with the horn button pushed.
Thread Starter
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Tuned
Joined: Nov 2007
Posts: 308
Likes: 5
Thanks for the info. My truck doesn't have a rag joint it has a small u-joint on one end and the original rubber booted bearing joint on the other so it might be more likely that the ground problem is in the column somewhere?
I will try try testing the horn relay tomorrow night after work to see if grounding that terminal with a jumper wire will activate the relay. And I will double check the horn button wires again.
so one horn brush should be grounded to the colunm and the other will be connected to the blue wire? Do you know if it is the right side or left side brush that is connected to the wire?
I will try try testing the horn relay tomorrow night after work to see if grounding that terminal with a jumper wire will activate the relay. And I will double check the horn button wires again.
so one horn brush should be grounded to the colunm and the other will be connected to the blue wire? Do you know if it is the right side or left side brush that is connected to the wire?
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
Thanks for the info. My truck doesn't have a rag joint it has a small u-joint on one end and the original rubber booted bearing joint on the other so it might be more likely that the ground problem is in the column somewhere?
I will try try testing the horn relay tomorrow night after work to see if grounding that terminal with a jumper wire will activate the relay. And I will double check the horn button wires again.
so one horn brush should be grounded to the colunm and the other will be connected to the blue wire? Do you know if it is the right side or left side brush that is connected to the wire?
I will try try testing the horn relay tomorrow night after work to see if grounding that terminal with a jumper wire will activate the relay. And I will double check the horn button wires again.
so one horn brush should be grounded to the colunm and the other will be connected to the blue wire? Do you know if it is the right side or left side brush that is connected to the wire?
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
There should only be one brush, which is connected to the BLUE with YELLOW stripe wire. That single brush is selectively grounded by way of the horn switch; the other side of the horn switch is grounded by the steering wheel, which is permanently grounded by bolting to the splined shaft. Later years have two brushes because there is no horn relay and the horn switch switches power instead of ground (unless you had cruise control).
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Posting Guru
Joined: Dec 2009
Posts: 2,134
Likes: 1
From: Mississippi
I also have a Grant wheel. If you have the one with the black horn button that has indents that fit the orange/brown fiber ring with the wire on it (hope that makes sense), it can be problematic; mine works when it wants too. The button will also pop out occasionally.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
1967/75 F100/250 4WD: The multi piece lower steering shaft & coupler assy connects to the input shaft of the steering gearbox with a clamp and thru bolt.
1976/79 4WD's have a one piece lower steering shaft and coupler assy. Connects to the input shaft of the steering gearbox w/a rag joint.
When you have a user name that reflects an F350, you should say "up front" in your first post, what you're working on.
1976/79 4WD's have a one piece lower steering shaft and coupler assy. Connects to the input shaft of the steering gearbox w/a rag joint.
When you have a user name that reflects an F350, you should say "up front" in your first post, what you're working on.
Thread Starter
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Tuned
Joined: Nov 2007
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In my mind I am picturing the the horn brushes in my 69 mustang which has 2 of them. I didn't get a chance to test anything tonight so results will have to wait.
F350 can be misleading, I'll grant you that, especially when I think of my f250 as a one ton after swapping 1-ton running gear under it
F350 can be misleading, I'll grant you that, especially when I think of my f250 as a one ton after swapping 1-ton running gear under it
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Here's what the turn signal switch looks like for 1975:
There appears to be only one brush. The picture is for a manual transmission; the automatic transmission version looks similar, the main exception being a provision for the gear indicator light. Both my Galaxie and LTD had 2 brushes, but that's because the horn switches switched power and there was no horn relay. 78-79 trucks are the same way if they don't have cruise control. The 77 and older trucks are a little different in that they have a horn relay with a single brush.
There appears to be only one brush. The picture is for a manual transmission; the automatic transmission version looks similar, the main exception being a provision for the gear indicator light. Both my Galaxie and LTD had 2 brushes, but that's because the horn switches switched power and there was no horn relay. 78-79 trucks are the same way if they don't have cruise control. The 77 and older trucks are a little different in that they have a horn relay with a single brush.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
Originally Posted by Fmc400
Here's what the turn signal switch looks like for 1975.
D3TZ-13341-A .. T/S Switch ~ Use with M/T without Speed Control.
D3TZ-13341-B .. T/S Switch ~ Use with A/T without Speed Control.
D5TZ-13341-B .. T/S Switch ~ 1975/77 ~ Use with Speed Control.
-----------------------------------------------------------------
1978/79 F100/350, Bronco & Econoline use 3 different T/S switches.
Thread Starter
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Tuned
Joined: Nov 2007
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Here's an update:
I grounded the Blue/yellow wire terminal on the horn relay like FMC400 suggested and could audibly here the relay clicking so that was good news.
I had the horns unhooked at the time and was using a test light to check for power.
Since the relay was working I removed the steering wheel to check the internal horn button wiring and when I pulled it off a horn button wire touched the steering wheel adapter and made the relay click again.
After I discovered that the horn button had only one wire connected to it I made a short ground wire to hook up to the horn button and everything works normal now.
I haven't had a working horn on this truck for 14 years!
Now I just need to get a schrader valve and plumb in my air horns
I grounded the Blue/yellow wire terminal on the horn relay like FMC400 suggested and could audibly here the relay clicking so that was good news.
I had the horns unhooked at the time and was using a test light to check for power.
Since the relay was working I removed the steering wheel to check the internal horn button wiring and when I pulled it off a horn button wire touched the steering wheel adapter and made the relay click again.
After I discovered that the horn button had only one wire connected to it I made a short ground wire to hook up to the horn button and everything works normal now.
I haven't had a working horn on this truck for 14 years!
Now I just need to get a schrader valve and plumb in my air horns