Automotive electrics fault finding sanity check

[Mike Tomlinson]

En el artículo , nemo escribió:

FORD: Found On Road, Dead.

[Andy Burns]

Getting old is a bugger, isn't it?

[Dave Liquorice]

And when you have brian rot not remembering things is a bit of a worry. My brian rot is supposed to just slow you down though not send you gaga.

[Dave Liquorice]

understand it

device

And it enables the use of a less heavy duty (aka cheaper) switch.

Slip rings are probably what are used but I'm sure there is a name for the unit that houses them on the steering column.

[David]

Thanks.

Answered further down thread about my wrong first diagnosis.

Likely options are the floating connection below the steering wheel (allows the wheel to be turned without tearing the wire apart) or the relay which protects the horn switch from bad things (also explained within the thread).

Cheers

Dave R

[David]

In this case the power comes to the horn push through a wire which connects to a big brass plate.

Pushing down on the horn push makes contact with another big brass plate which is earthed to the steering column.

I originally explained this in my OP but took it out because it looked too bulky and convoluted :-)

Besides which, I am testing the wire coming into the horn push, not the horn push itself.

However, thank you for the idea.

Cheers

Dave R

[David]

Thank you TNP for the term "slip ring".

This is at the top of the list of suspects. Along with the relay to protect the horn switch.

Now waiting for the 24mm socket (to remove the steering wheel) to be delivered from Amazon.

Cheers

Dave R

[David]

Yes - slip ring coming up again as the main suspect.

Once I get a 24mm socket I can take the steering wheel off and check.

Cheers

Dave R

[David]

LOTUS: Lots Of Trouble Usually Serious

[Mike Tomlinson]

En el artículo , David escribió:

Wouldn't checking/substituting the relay first be a better idea, as well as being easier to eliminate? The horn is a nasty electromechanical thing which will cause a lot of arcing on the relay contacts, making it prone to early failure. I think it unlikely the slip ring is the problem.

Testing the connections with the relay out is easy. Do these with the ignition on.

Jumper the contact pins with a paperclip and the horn should sound. Put a meter across the coil pins, you should see battery voltage when the horn button is depressed. If not, check one pin is at battery voltage wrt chassis. If that is missing, you have a broken connection or blown fuse (no +12V supply to relay coil).

Now check the other coil pin has continuity to chassis when the horn button is pressed, if this doesn't happen, you have a break between the relay and the horn button.

It took me longer to write that than it would take you to do those quick checks.

[Lee]

Bear in mind that the horn push switch may be "grounded" through the relay coil *not* straight to ground - unless you can see that it does otherwise. If the relay coil is open circuit (uncommon, but happens), then it will look like a wiring fault...

Remember to be careful if it has an airbag :)

[Lee]

Doh!, looking at the wrong wiring diagram* - thought it was somewhat unusual to do it that way :)

*much earlier Fiat, shows the horn being powered from the stop light switch supply and the relay in the earth return from the horn push...

[Lee]

Ok, if you have access to the back of the switch already, shouldn't grounding the wire (to a proper separate ground of course) sound the horn? If it still doesn't, and the 12v is present, then it's not (just) the slip rings...

[tony sayer]

Fix or Repair Daily

Lots Of Time Underneath Servicing;!..

Or as Colin Chapman the lotus factory owner once said;

"If it hangs together for more than the one race, we've built it too well"

[David]

Slip ring is underneath the base of the steering wheel - you need to remove the steering wheel to get at it.

12V is not present at the wire directly behind the horn push.

Cheers

Dave R

[David]

As with the better mouse trap - first catch your mouse. Or the ten best ways to cook a bear - first catch your bear.

I have a large number of relays under the passenger side lower fascia - can't remember the number but I think it is between 7 and 10.

I am waiting for someone to tell me which relay it is, as I don't have any documentation which includes this.

Also, according to the Fiat forum in the Ducato section having poor or no contact via the slip rings is a known common fault.

Cheers

Dave R

[Lee]

Ok, I misread that it was.

[David]

Just to confirm that the fault was the contacts under the steering wheel and I now have a tooty horn again.

I also seem to have cleared the problem with the self cancelling being sticky/awkward, which suggests the last person to take the steering wheel off didn't line the pin up properly.

Anyway, thanks to all for the advice and assistance.

Cheers

Dave R