ASD troubleshoot. 8 flashes on diagnose
 

I diagnosed my ASD and it flashes 8 times, giving me a bad brake sensor or a magnetic switch of some kind. If the brake sensor is ok, what kind of work am I looking into on the magnetic switch? Is this something that can be opened and cleaned or should it be replaced? How can I troubleshoot it? btw, 1990 300te

Any experience is highly appreciated! Winter´s coming up, I need my ASD... :)

Thanks!