[Lee T]

I may be leaning towards relay over the coupler as it's a simpler job, with a normal relay. I will try your suggestion and unplug the coupler. If it's not that it at least narrows the search.
Can't say I remember a horn relay failing but I have replaced failed ones and even reliable relays can and do fail.
I can only find references to a pcb the relay is soldered onto. Explains why I couldn't remove it.
Appreciate any and all suggestions, unplugging the coupler was a good one and I'll post the results asap hopefully with an answer. There's lots of posts of horns not working but not one with my cars symptoms, so yes it will be interesting to find the cause.

Thanks. Lee