Sherlock Holmes & the Case of the Wayward Horn
Set about rectifying my lack of horn.
Switch OK. Other wiring looked a little flimsy. Dived into the very cramped space and whilst attempting to strip a bit I (a) ripped open the back of my hand and (b) damaged one of the indicator wires.
It happened to be the 'wrong' one which earthed out thereby breaking the fuse.
Unfortunately, the horn and indicator fuse is also the one from which the alarm is piggy-backed so it went wild. Where did I put those fuses ?
Dash out, turn alarm off, dash in search for fuses, repeat.
Eventually, one nail and one hand dressed and healing, one horn working. I'm knackered.