Hi ppl,I have an issue on fd when I switch on the rear window heater and the lights are on the horn comes on also.

any help please

 

ok does switching the window heater or lights on it's own make the horn go off? Or only when heater AND lights are turned on together?

 

Yes,when they are on together and also when I turn the ignition on the break lights are on.

 

unfortunatly I would begin by tracing wires, very fiddly and annoying job but you could have a short or crossed wires somewhere. Perhaps something non oem was tapped into an electrical source causing this issue. Pull the centre console and the steering cowling covers off and start tracing the wires from the respective buttons and see if there's anything untowards. Under the steering column and towards the fuse box should also be inspected. It's the only way

 

Any stereo installs lately? remote start? basically what's changed before the issue started? looks to me (very high overview) that your lights and accessories circuit somehow got put in with the defrost/AC wires, so when pressing the break or turning on the ignition "completes" the circuit for the horn. Curious to know if you pull the fuse for the horn does it still go off when switching the lights and ignition?