My sons 2003 Fiat Punto Active 60 8V failed its first MOT 'cos the horn has
suddenly stopped working. I've checked out most of the circuit and need some
advice. The horn push is working fine, and the horn itself works when I
short across the power side contacts at the relay base. From the steering
column horn push contacts back to the relay base I have a continuous circuit
when checking using my multimeter although the resistance is high at 38 Ohms
(or 60 swapping the leads around). When the battery is connected I find that
the horn push circuit has 7.8Volts across the relay base connections whilst
the button is not pressed! When I press the horn button the voltage
increases to 11.8Volts (relay not connected). I have checked the relay
itself and it appears OK and have tried swapping it.
I suspect that there is another "component" or device in the circuit
causing the 7.8V to appear which is creating the fault.
One further thing, I see that the horn push button wiring disappears within
the steering column into a circular box directly underneath the airbag/horn
circuitry. This box carries the stalks for the wipers indicators and has a
number (735337940) on it. Googling tells me its a "PUNTO FL . 2003 1242 8V
CF3 SOUND ACTIVE DYNAMIC" whatever that is! Could this be creating the
Any advice on what may be causing the problem and how to repair it would be
Is one side of the horn relay coil 12V (quick meter check) if so it is probably
a 12v relay and should pull in when the other side of the coil is grounded
through the horn button, and the horn should sound.
Check also a wiring schematic for the car, Haynes manual, or
If so you might consider isolating the lead to the horn button,
and running a single core to the relay.
There are usually enough grommets in the bulkhead to take
another single core.
Get the MOT and diagnose at leisure.
I ran for weeks with a toggle switch in place of the "start"
position of the ignition switch (burnt contacts) delay in
sourcing a replacement.
Fiat are notorious for bad contacts, often due to push on blade
(Quick and dirty way is to solder a lead to a pin, push through
wire, bend ends back parallel to wire, tape generously to
insulate, saves cutting wire, there are also insulated IDC tap
Thanks for the reply. I think that the problem is within the "black box"
mounted underneath the horn contacts. I understand that there are rotary
sliding contacts for the horn and other circuits.I'm not certain what it's
called! I will be acting on your advice and will temporarily bypass it for
the MOT and then either replace the unit or if it's funny money I'll stick a
switch in elsewhere,
For those interested, I finally repaired by snipping the wire at the
clockspring and also at the engine fuse box and then running a new wire
bypassing the old one. There must have been an open circuit somewhere. Only
problem now is that I've got the airbag warning light lit all the time
now!...........yes I know that this is a known fault and the dealer can do a
mod for X quid!! At least I've got it through the MOT!!
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