I have exactly the same issue as you. The horn stopped working and it was not dependent on the lights being off or on. I have a Zafira B which is now 16 years old and it isn’t worth repairing the CIM module. However what I have found is, isolating the battery for a few hours brings it back into operation for several hours, just enough to get it through an MOT. Once through I can see if it’s worth tinkering with

I took the connector off and soldered wires on insted.. no more messing about that way

I have the same problem where my horn doesn't work. When press it turns the volume up on the sterio. Work without lights on but when lights are on, the horn don't work. It's happened twice now an both times I've fixed it for a couple months just by removing the casing and unplugging the connector from the cim unit. Clean it out and push back in firm. I think it may just come loose when going Iver harsh bumps ect. When I read up about it it's to do with a small peice of plastic that snaps off so again, might be important peice that keeps the connector nice and snug? Since fixed it twice that way it isn't a concern for me anymore. Recommend to just unplug and give it a clean an make sure its in. Saves messing with the ofcom ect. Pricey peice of kit

NICE ONE LAAAAAAA

Why does the horn sound like that?It sound much better in my father's astra h

The horn is so dinky