Mystery drilled rear disc and sensor.

[6speedmanual]

On my BX Sport, the RHR brake disc has a series of 8 holes drilled through the disc. Mounted off the caliper is a bracket with a some sort of pick up (hall effect sensor maybe?). The wire disappears over the rear beam frame towards middle of the car. I have yet to trace it any further.
It looks home made. It could potentially be used to measure road speed.
Any ideas what it might be for?
Previous owner - Hilary Stone - maybe knows what it is?
Thanks
Pete

Sport RHR brake. Copyright 6speedmanual 2024

[xantia_v6]

Cruise control speed sensor?

[6speedmanual]

Cruise control speed sensor?

Good idea.
But no cruise fitted on the car (maybe removed?)
The wire goes through the floorpan to under the rear seat. Then under the carpet. Haven't had time to pursue any further just yet

[Kitch]

Have you lifted the back seat to see if there are any clues? Does the speedo work? I'm wondering if it failed and someone used an electric one or something? Either way, those are big holes to have in a thin brake disc!