brake light switch

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have fitted 2 brake switches recently but still getting engine workshop/coil light flashing,and only code is for the brake switch both times.it is the white 4 pin screw in type,which seems simple to fit,any one any suggestions as to what might be wrong?cheers adam.also there seems to be a coincidental slight binding of brakes whenever the warning light kicks in,have asked before but can a brake light switch fault actually affect the preformance of the brakes?ta