On my 1975 F-250 4x4, my horn is not working. Here's where I'm at with troubleshooting. Looking for advice on next steps.

I tested a jumper wire from the positive battery cable to the single wiring blade on the horn and got no sound. I took the horn off the truck moved the pitch screw a bit and made sre there was no loose junk falling out of the horn. Retested, still no sound.
I bought another low tone (passenger side) horn and did the same test, jumper wire from the positive battery cable to the single wiring blade on the horn. This horn works!

I have a stock steering wheel but a 1978/79 style power steering gear box. I've read about the need to have a jumper across rag joints to make sure the steering column is grounded to the frame but I don't have any rubber "rag" joints. To rule that out I built two jumper wires, one for each joint on my steering shaft.

Here's my lower jumper close to the steering box.


My upper jumper is like this one that @julianfisher built for his crew cab.


I have the horn relay on the passenger side fender and here is what I have come up with in testing it.
The front left (passenger side) spade connector with a yellow wire has ~13.75V all the time, as it should. (Hot-at-all-times power goes to the relay through the YELLOW wire, perfect!)
The rear spade connector also has ~13.75V with the key off.

If I use a jumper wire to apply power directly to the front driver side spade on the relay, from the positive terminal on the battery, the horn will honk.
If I use a jumper wire from the rear spade connector to the negative post on the battery, the relay will click.

All these tests are with the 3 wire connector still connected to the relay but loose enough for me to get a voltmeter and/or jumper wire in place.
I have another relay on hand that exhibits the exact same behavior so I think both relays are working. Is this correct?

My positive power spade on my steering wheel does not have 13.75V. It has pretty much no voltage.
I think this troubleshooting advice from @fmc400 describes the point I'm at right now...

"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."

If I run a really long jumper wire from the female spade for the BLUE with YELLOW stripe wire which is the rear connector on the 3 prong terminal, and extend it into the cab and do a continuity test between the end of the BLUE with YELLOW stripe wire I've extended into the cab to the male spade on the steering wheel I DO NOT get continuity. Is my problem in my blue with yellow stripe wire not having continuity between the relay and steering wheel?

Thx

 

I would make a long jumper wire, and test continuity from the steering wheel, down the column to the steering box. Maybe the steering box is somehow not grounded?

 

when you ground the rear terminal and the relay clicks, your horn(s) should sound assuming they are connected and grounded...at minimum you should see battery voltage show up on the wire going to the horns as long as the rear terminal is grounded (closing the relay contacts).
Does the horn relay click when you press the horn button?

 

Thank you for the suggestions!

With some further troubleshooting, it appears that I have two problems compounded together that need to be solved before my horn will work as it should.

First, I don't actually have a horn button so I've been using a jumper wire from the male spade on the steering wheel that I ground to the dash to eliminate steering column grounding as an issue. The fact that my horn male spade has no voltage is my first problem.

Second, when I ground the rear relay spade all I get is a clicking sound using the stock wiring and original relay.
To test the health of the relay I ran a new long jumper wire from the rear relay spade to the steering wheel. I verified that the wire had 13.75V in the cab and ground it to both the steering shaft and the dash. In both instances, I could hear the relay click but the horn did not sound.

I unplugged the wiring connector at the relay in the engine compartment and did a continuity test with the long jumper as an extension to the rear female spade in the harness with the jumper wire running back into the cab close to the male spade on the steering wheel. This did not pass a continuity test. Huh!

I wasn't sure that either relay I had on hand was good so I picked up a brand new relay at the auto parts store and performed the above tests all over again.

With the new relay installed and only the original wiring in place, I still did not have any voltage at the male spade on the steering wheel.
I again ran the long jumper wire from the rear relay spade to the steering wheel. I verified that the wire had 13.75V in the cab and grounded it to the steering wheel. Viola the horn sounded!

I unplugged the wiring connector at the relay in the engine compartment and did a continuity test with the long jumper as an extension to the rear female spade in the harness with the jumper wire running back into the cab close to the male spade on the steering wheel. This again did not pass a continuity test...

So I had a bad relay which was taken care of by replacing it. I've definitely learned that a clicking relay means jack squat! In this case for my horn and back when my A/C blower motor stopped working last summer the relays would click but the systems they worked with were not functioning properly.

At this point, all I have left to do is troubleshoot the Blue with Yellow stripe wire which is the rear connector on the 3 prong terminal and runs to the steering wheel male spade connector. Once I figure that out I'll have a working horn, via a jumper wire that will act as my horn "pad" until the vendors get the correct ones back in stock. (Most everyone seems to not have them in stock right now)

 

The steering wheel horn male spade, circled in blue should have 12+ volts at all times right? That is the final piece of the puzzle I am trying to solve.

 

I just went through all of this, but my setup was a little different. I don't have a relay. However, inside the steering wheel, I found one of the pins is hot and the other is ground.

 

I've narrowed down my wiring problem a little more.

I got in with a test light that I grounded to the dash and started to poke it into the connectors on the steering column side of the steering column to main wiring harness half moon-ish looking connector, while it was still connected up to the main harness.

I forgot to mention earlier that I have a 1973 steering column in my 1975 truck from when I did my manual to automatic transmission swap. This column has wiring and a switch for cruise control on the turn signal stalk.

When I touched the test light to the lower, right of center, inside wire, the horn sounded.

I then grabbed my multimeter, put it on the continuity test setting, disconnected the steering column connector from the main harness connector and checked the main harness side of the connector pin in that same lower, right of center, inside wire spot for continuity. I did get continuity between that point and my long jumper wire that I had run from the rear horn relay spade in the engine compartment.



A continuity test between the steering wheel male spade and the lower, right of center, inside wire on the steering column side of the half moon-ish looking connector did not give me continuity, so I know my wiring break is somewhere within my steering column wiring.

 

At the beginning of your post, had a hunch it was between the half moon connector and steering pad horn male terminal. If you're able to zero in where the break is, consider cutting say an inch piece out and replacing, but solder the connections. While you have the half moon connector disconnected clean both ends with electrical cleaner or a similar product (brake clean / rubbing alcohol) and use dielectric grease when putting them back together. If you're connector side latches brake or have broken off, use skinny wire ties to keep that half moon connector from coming apart. Sorry if you already know this from the earlier manual to automatic transmission swap project.

 

I pulled my steering wheel off and used my voltage tester to check that I have continuity and the full 13.75V all the way up to the horn brush that is part of the turn signal assembly.

My horn brush is simply not contacting the ring on the steering wheel. My steering wheel is cracked pretty good so maybe that has something to do with it.

I played around with adjusting the steering column up further into the cab by loosening the collar clamp in the engine compartment and the two 1/2" bolts that hold the column up against the dash to the point where the steering wheel was touching the top ring of the steering column, but the brush and ring on the steering wheel never contacted each other.

First, I'm going to replace my turn signal assembly. My right cancel arm is broken off so I might as well bite the bullet and replace the whole turn signal assembly with a NOS one since I found it for a decent price. I don't think my horn brush is worn too much but I'll be able to compare the one on the truck to the NOS one when it arrives.



Nothing like troubleshooting a problem to learn how to repair something that you've never done before.

 

D3TZ-13341-B NOS "Hazard Wrng Sw" / Turn Signal Switch Assembly arrived today which fits 1973 - 77 trucks with automatic transmission.



Hopefully, I'll have time to get it installed soon.

 

Installation really isn't too bad.

Here is my post about it:
https://www.ford-trucks.com/forums/1...l#post17903778

 

Thanks @meangreen92! I bookmarked your post when I came across it last week. Thank you for the excellent write up!

 

Anytime! I wish I'd gotten an OEM switch, but I got a repop from David Carpenter, and it doesn't click when turned on or off, as loudly or solidly as the original one did.

 

I was fortunate that a NOS one was available and not asking an exorbitant price on ebay when I went looking.

I didn't think my horn brush was too worn but in comparing the new horn brush to the one on the truck I can definitely see that the horn brush on my truck is worn.

My horn right now is a jumper wire pushed into the steering column side of the half moon connector, running up the steering column and tied around the shifter lever. I just touch the bare wire to the shift lever if I need to honk the horn. You can kind of see the red wire in this picture:


My truck has only been in the driveway since I hooked this up so it'll probably not see road duty like this unless I decide to go for a drive tomorrow.

 

I replaced the Hazard Warning/ Turn Signal Switch in my truck today. Here's the old and new next to each other before getting started:



I unplugged the half moon connector under the dash, removed the red wedge, and used a small pick to release the small tabs that hold each wire in the connector one by one. I then followed the directions that @meangreen92 posted in this thread - https://www.ford-trucks.com/forums/s...8&postcount=56.


I taped up two different wires to be my pulling wires for the 9 new wires as I pulled them back down into the column. Here they are after being pulled through while removing the old switch and wires.



I pulled 4 wires down on the first pull. On the next pull I did two wires from the new switch and re-pulled the red pulling wire that I'd just used back down the steering shaft tube as well. That left me with one wire left to pull the final three remaining switch wires. When I taped the wires together I did them side by side so they were easier to pull through as opposed to in a clump.

The new switch assembly and horn brush is installed. Here's a close up of the horn brushes to show the worn one vs. new one:


I still need to fiddle with the horn brush to steering wheel gap, which may just be solved by getting a different steering wheel. At this point my turn signals cancel properly now, which I'm happy with, but I'm still using a hokey jumper wire for my horn.