Tripmeter sensor qn for Elec Eng types

[obrut]

my rally car has a VDO "mini cockpit" tripmeter for measuring stage distances etc.

the tripmeter receives a signal from a cable drive sensor unit that sits between the speedo and the speedo cable. the cable is rotated by the gearbox and, i assume, causes a magnet or similar to be rotated past a sensor.

the problem with this system is that if the speedo drive cable fails then you lose the signal to the tripmeter (as occurred during my last rally)

other brands of tripmeters use a sensor probe that mounts near a wheel stud. the rotation of the wheel thus causing a signal to issue.

do you see any problem in setting up my unit to work with a wheel probe (as a backup system)?

how can i measure the output of my cable drive sensor to ensure i get a compatible wheel type sensor?

anyone have any ideas?