The OVP is just a fancy fuse. It either conducts or it doesn't. Look at the wiring diagram and view the circuit from the OVP to the controller. See if it goes somewhere easier to verify, or mount a test wire to the power wire input and wire it to a multi meter and the next time the light is on verify whether you have power. It is really very simple.
If it has power the problem is elsewhere.
Bosch Master, ASE Master, L1
33 years MB technician