electrical and ignition Horn circuit puzzle

[Mike Self]

I'm stumped.  My horns decided not to work, so I went a troubleshooting.  Figured it was the relay so swapped it out for a known good relay.  No good.  So I delved further.  

 

Here's what I've checked so far:

 

*  relay terminals 30/51 (power source) & 86 (trigger) are both hot with the ignition on

*  terminal 85 (ground) shows continuity when I ground the horn slip ring (on the steering column) to the steering column shaft, which is grounded to the body.  Thus the wire connecting the horn push on the steering wheel to the relay is good.  2002s have a grounding system for the horn--the steering wheel horn button (or push) grounds the relay, thus completing the circuit and causing the horns to blow.

* running a lead directly from the battery to the green/yellow wire at the relay (that goes to the horns) causes 'em to blow, so the horns themselves are good

* there's continuity between the horn button and ground when you press the button.  

* tried several different tested and known good relays

* with all the terminals connected to the relay except the ground wire, I grounded terminal 85 to the battery.  That should have completed the circuit and caused the horns to blow.  It didn't.  

* with all terminals connected at the relay, I manually closed the points on the relay (I have the cover off).  No spark at the points (which would indicate current flow), and not a peep from the horns.

* I have 12 volts on both sides of fuse 8, which contains the horn circuit.   And the fuse itself is nice and clean.  

 

I'm outa ideas.  What have I missed?  

 

TIA

mike

 

[jimk]

with all the terminals connected to the relay except the ground wire, I grounded terminal 85 to the battery. That should have completed the circuit and caused the horns to blow. It didn't

Relay seem bad because when you power the horns on the relay output side, the horns work.

[cda951]

Have you checked for voltage drops on both the power and ground sides of the circuit?

 

There could be a flaky connection somewhere in the circuit that is not allowing sufficient voltage to activate the horns.

 

Chris

[Mike Self]

Thanks for the ideas--I did check voltage and I have 11.6 volts at the relay--same on the terminal and then on the frame of the relay that carries the current.  

 

And I did try several different relays that I tested by connecting 'em directly to the car's battery; they work fine.  

 

More ideas?

 

mike

[ray_]

 

I think the problem must be bad continuity somewhere between the horn button and the relay.

 

Take a known good ground and attach from the relay input, progressively working backwards until the horn doesn't work. And there ya go!

 

Cheers,

[rstclark]

My horn recently quit working along with the radio.  the problem was a perfectly good looking fuse  in Number 6  not  8   but  maybe your fuse box is different.  A new 8 amp fuse did the trick for me

[Mike Self]

On a '73, the horn is on fuse 8, along with the brake lights and several other things, all of which work.  And my voltmeter showed 11.6 volts on both sides of the fuse.   And Ray, I connected all the wires at the relay (a known good relay--I tested it) and then ran a jumper wire from the ground terminal on the relay to the - terminal on the battery.  That bypasses the ground wire running from the horn button to the relay, and should have made the horns blow.  It didn't.  

 

Still stumped

 

mike

[Simeon]

Have you verified if the relay operates when the button is pressed?

Assuming it does, is there any adjustment screws on the horns? How about if you give that a twiddle? The horns are obviously electro-mechanical mechanisms and if there is an issue with the internal contact which cuts on and off you might find that they don't necessarily draw a current when connected.

Why they would work when direct connected but not via the relay? Volt drop in factory wiring? 11.6v seems a bit low (though that on its own wouldn't be it). Combined with a few ohms here and there you might not have sufficient voltage to operate the horns.

[ray_]

Ooh. I missed that last bit.

 

Swap the horns to your other '02 and see if they work!

 

Good luck,

[Dave3x72tii]

try running your b+ jumper to the 30 terminal of the relay and see if it honks. if the relay doesn't click when you ground it. it may be that the original relay was bad and the test relay has a different terminal orientation than original, or it is a diode equipped relay, a non diode relay doesn't care which is 85 or 86, but I think a diode relay grounds through 86? 02 lamp and possibly horn relays are oriented differently than generically supplied horn/foglight etc. relays

[Mike Self]

Fixed it--and I feel kinda dumb...my original diagnosis was correct:  the relay was the problem--it finally died after only 42 years.  But I caused the diagnosis problem.  I had sketched out a wiring diagram and inadvertently reversed the location of the trigger (hot) lead and the load lead and guess what--it doesn't work that way.  I finally figured it out, reversed the wires (with a new relay) and honk, honk.  

 

I'll doublecheck my diagrams before deep delving next time..

 

mike 

[im3crazy]

I agree with Dave3x72tii.  I've had diode relays that caused the same result, and have seen installed relays that were supposed to be identical only to find out on close inspection that the terminals were different.  I've also found relays installed backward, which I thought could not be done.

 

I've also had base terminal failures due to poor contacts resulting in heating, crystalization which lead to high resistance and failure.

 

Examine the relay markings to deterrmine if it's a diode one, or use voltmeter in ohm position and take the readings to determine if current will flow only one way.

 

Attached are two relay images that might be helpful.

 

 

[Mike Self]

Unless it was replaced by a PO, there are no relays on a 2002 that contain a diode.  They're all plain electromechanical relays utilizing an electromagnet to close a set of points.  On roundies, this relay is a metal can about 1 1/2 inches in diameter, and lives between the brake fluid reservoir and the voltage regulator.  On squarelights, it's a square relay that clips into the bracket in the same location, along with relays for the headlights.  

[Dave3x72tii]

but replacement relays often do have a diode where the original did not even from bmw

[carpainter]

I have been sorting out a 1974 2002 with an inop horn.

I touch the yellow green wire to the battery and the horn blows fine.

I finally read your thread about the 3 relays on the left inner fender and switched them .

still no horn but, one time I heard a clicking so I sprayed the terminals and got it kind of squeaking.

when I wiggle the relay on the right, it tries to work.

I guess next move would be to replace it. Where do you get one?

The local dealer had no idea .duhh

o