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 fault?
Any advice on what may be causing the problem and how to repair it would be appreciated,
regards,
David