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Fixing the horn on a Falcon ute

My father owns a 1978 Ford Falcon utility and I have a question relating to the vehicle’s horn. The horn must’ve worked at some stage early on in the vehicle’s life but it now doesn’t work and hasn’t worked for 30 years or so. I wonder now whether the horn may not have even been connected up from new or could it be possible for the horn to stop working due to constant use?

My father also drives trucks for a living and he had the horn in one of his trucks disconnected because it would sound without even being activated. Is there an easy answer to these questions? (K. C., Wangaratta, Vic).

Horns are electromechanical devices that have an electromagnet and electrical contacts. Normally, the con-
tacts are closed and when power is applied to the horn from the horn switch in the cabin of the truck, the magnet bends a sheet of steel towards it.

This also causes the contacts in the horn to open and so the magnet power is released and the steel returns to its normal position. This restores power to the magnet and the process starts again. The movement of the steel sheet is what creates the sound.

They can usually be repaired by cleaning and adjusting the contacts. Sometimes it is the horn switch in the truck cabin that is at fault, where it does not make contact when pressed or it is too sensitive and sounds the horn when not required.

If you’re not confident about doing it yourself, the horn and wiring can be easily fixed by an auto electrician. In any case, replacement horns are readily available from auto accessory stores.

FM transmitter for drive-in cinema

I am helping a small country shire re-open their drive-in cinema which is equipped with an old version of your Minimitter made in 1992. It is hopeless at staying on frequency which is more than compounded now with most car radios using precise frequency tuning, ie, exactly on the spot.

I am looking at replacing it with your 2002 design and would like to know if this version is stable enough to be reliably picked up with modern car radios. We are running an AM transmitter which is spot-on but the AM end of most car radios leaves a lot to be desired in terms of response – not that these old Australian-made Raycophone projectors go much past 7kHz in terms of the top end. But they still spit out a good screen image over a 100m throw onto an 18m screen and they are still running carbons. (L. M., Darlington, NSW).

The December 2002 design is crystal-locked so there should be no drift problem.