FrenchTF

I'd be very grateful for some thoughts and advice on a problem that I have to fix in the next couple of weeks before the bi-annual CT.
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Actually the horn's very intermittent - just suddenly worked every now and again at random and unexpected times and now hasn't worked for a while. No pattern established so far.
The horn itself seems OK and works with a separate 12v supply.

It's an early (November 2002) TF with the Lucas fob. Lots of lurking and Googling is leading me to the Rotary Coupler or perhaps a relay on the BCU (apparently a common fault on later units) but any thoughts would be welcome and if it's one of those which would you suspect most and which is the simplest to fix?

If it's the coupler can it be something like a bad contact or do they just die and need replacing? I think I have been well warned about the airbag but any other hints would be much appreciated