The brake light switch is right above the brake pedal (or real close to it). It activates when you press the brake.

I believe that it is used to signal the ABS that it's OK to activate, as well as turn off the cruise control.

I was getting an ABS light and replacing this switch fixed the problem. Takes about 5 minutes. Or 15 minutes if you're outside in the dark (like i did).

This is the cheapest and easiest 1st step towards fixing your problem. i think that the part is around $15.

Regards,
Troy
1995 E420