Brake sensor 944 S2 Cab
 

I have a 1990 944 S2 and have issues with a brake sensor. First off none of the computers could pick up information off the car itself so trial and error pointed out to one sensor and it was replaced. the warning light still comes on. My mechanic has replaced the sensor on all 4 wheels now and still the light comes on. He thinks it may now be the relay. Has anyone else had this issue and know how to resolve it?