brake pressure switch on 1990 GMC Suburban 1500

The brake service light stays on all of the time. Is this an indication of a bad pressure switch? I notice that there is a "port" on either side of the pressure switch, what are these for?

Asked by for the 1990 GMC Suburban 1500
First, check your brake fluid level, if it is low that will set the light. If the fluid level is ok, then it can be several things. Have a good shop Diagnose this issue to be safe.

here are some shops http://repairpal.com/directory?address=80631&car_brand_names=GMC
if you dont know , dont mess with it. too many people kill others thinking they know how to fix critical systems.. besides you'll live longer if you do take it to a real break shop or the dealer..