Connect one side of the horn to one side of the 12v battery. Connect the other side of the battery to the metal of the car body/frame. Connect the other side of the horn to the button, and the other side of the button to the car body/frame.

Thanks Peter and Andrew, this cheap horn now gives a (non A7 sounding) AOOGHA so I'm legal again.

Location: Near M1 Jtn 28

Brian. Have you considered a small 6 to 12 volt converter installed onto your 6 volt battery. This way you can use your 12 volt stuff off the one battery. The advantages being that you do not require a second battery or the charging of it. I use one to run my 12 volt satnav. They cost around £10 from ebay and are the size of a match box.

John Mason

Location: Nottinghamshire

Many thanks John, I didn't realise that such things existed. I used a separate 12v battery because I had one spare and I'm not very good with electrickery (as one member puts it).
I'll have a look around for one of those gadgets.

Location: Near M1 Jtn 28

Be careful, a horn may draw more current than one of those 6-12v converters can safely deliver.

A satnav will draw a low current compared to a horn.

I had a problem with the armoured cable shorting out and had apparently fixed it but now it's back and the aluminium armouring shorts out on both the 6v and 12v circuits.
I have already insulated both ends of some cables and will do all the other cables and look for any areas where the middle of the armouring may be touching a live connection.
I'll get there eventually!!

Location: Near M1 Jtn 28