No horn - where to begin?

[cptmoney]

So I have a 1978 2wd half ton....that has no horn.

Actually, it's got a few things that need ironed out, but this seems like it would be in the "low hanging fruit" category - so I thought I'd try and knock it out first.

Where do I begin to troubleshoot them?  How do I even test the horns themselves?

If I apply a grounded source of 12v power to them, they should work - correct?  Is this a good start?  I can see the horns and the wiring coming from them...so I know they're on the truck and in place. 

The horn button itself is off the steering wheel; should there be power to the metal plate? 

Where do I begin on all of this?

Need a picture of my fuse block?  From under the dash?

Thanks in advance for your help!

[bd]

What do you mean by a "grounded source of 12v power?"

The 1978 model didn't have a "horn fuse."  The horn relay received power directly through the fusible link attached to the firewall junction block in the engine bay.

Unplug the single green wire from each horn.  Momentarily jump B+ from battery to each horn using a 20-amp fused jumper wire.  Each horn should sound.  This will tell you if the horns are functional without starting a fire.  While you're there, clean the dirt and oxidation off of the horn terminals with a small wire brush or equivalent and spray WD-40 into the wire connectors of the harness.  Plug/unplug the wires to each horn half-a-dozen times to improve the electrical connections.

You indicated the horn button is missing.  Are you referring just to the cover or the steel cup and spring plate in the top of the steering wheel?  If the steel cup is present, press on it and listen carefully for a muffled click under the dash.  If you hear clicking, the horn relay is installed and at least trying to supply power to the horns.  Use a test light and check for power on the wires that connect to the horns while a helper pushes on the 'cup.'  If there is no sound when pushing on the cup then look for the 3-prong horn relay hanging out of the harness near the fuse block or adjacent to the steering column (or a vacant 3-prong socket with red, dark green and black wires).  If the relay is missing, probe the red wire for B+.  The dark green wire feeds power to the horns and the black wire is the relay ground from the horn button in the steering column.  See the 1978 Wiring Manual for details.

[fitz]

  As far as the missing horn parts on the column, Captkaos did a great write up on how to fix a loose tilt column.  There are lots of pictures to show what parts should be there.

[cptmoney]

By grounded 12v, I just mean that if I grab an extra battery, I can ground the negative side and utilize the positive side to test the horns.  That's what I did, and it worked out just fine.

So.....here's what I've learned so far: the horns themselves work perfectly.  When I tested them with the extra battery, both horns worked fine.  Sounded good and strong!

Working back, I replaced the relay.  I was hoping that it just might be that simple....but a new $7 relay proved to have no impact.  That's not the issue.

With the relay out, I used a jumper wire to reach from a "hot" fuse terminal to bridge over to the horn relay...and the horns worked perfectly. 

So - what's next?  I have no power up the column then....is that a reasonable assumption?  How do I test for power up at the actual horn button?

And for what it's worth - I am missing just the horn button "cover" - not the spring-loaded plate and steel cup.  All of that is still in place.

Any input?  Thanks again for all the great advice!

[bd]

Ground the black wire at the horn relay and the horns should sound.  Once verified, use a test light clipped to ground and probe the spring plate under the cup - the test light should illuminate.  If not, there is an open circuit between the relay and the spring plate, which in fact is the horn switch.  On the other hand, if the test light illuminates, remove the cup, spring plate and spring loaded plunger for access to clean the metal bowl of the steering wheel and remove any rust or dirt.  But, be careful to avoid damage to the plastic shoulder at the outer circumference of the spring plate which serves as an insulated seat for the plate.

The black wire running between the relay and the horn switch provides the ground path to energize the relay when the horn switch is closed.  The actual circuit path is from the relay ground terminal via the black wire, through the flat turn signal connector alongside the lower column, up the column to the turn signal switch and its integrated copper brush, through the turn signal cancelling cam contact ring, through the spring loaded plunger, to the spring plate.  When the spring plate is distorted to contact the central metal ring or shoulder of the steering wheel, the relay ground is completed energizing the relay, and the horns sound.  Rust at any of the contact points or a worn out turn signal switch brush will interrupt the ground path.

So, now you are an expert.   

[87slammer]

The horn contact at the steering wheel is a ground. When you press the horn button the the circuit is completed and pulls in the horn relay contact. That allows a full 12V the go to the horn. To test the individual horns take a 12V source and touch the connection at the horn. The horn should work. If it does either the relay or the horn button contact has an issue.

[cptmoney]

So.....after a little cleaning (thanks for the tips, bd!) - the horn came right to life!  Wahoo!

I did the grounding test...started chasing power - and voila!  A little cleaning up near the spring plate/steel cup combo - and BAM!  We're live!

Thank you so much for your input, all.  I am genuinely grateful for the help!

[bd]

You are quite welcome!  I'm pleased I was able to help.