What's this wire for?

[Steve_T]

Firstly, is that a 3-pin connector on the end of that wire?

Secondly, trace (visually) where it goes - does it go up to join the loom which connects to the alarm control module (mounted above the pedal box)?

If the answers are yes and yes above, then it is the connector for the optional glass break detector for the alarm system. The alarm doesn't come with that, so usually that connector is just zip-tied up out of the way - yours has obviously fallen down - just zip-tie it back up to the loom somewhere out of the way. I'm assuming of course that you don't have the glass break detector installed on your alarm.

Let me know if it is not this but I reckon it's a good guess.

Steve.