Pretty sure it's connected to the base of the parking brake handle. You have to remove the center console/armrest to get to it.
Before you do all that though, have you checked the fluid level at the reservoir? If it's low, before you jump to any conclusions and top it off I suggest you start pullimg wheels off and check the brake pads. As they wear, the caliper pistons rest further outside of their bores and the fluid level in the reservoir drops because it's all in the lines amd calipers. If you simply top it off and move on with life, next time you go to replace brake pads and in doing so compress the pistons back in it pushes that fluid back to the reservoir and spills out due to the system being overfilled.
Also check the electrical connector at the reservoir, make sure it is securely hooked up and the wires comimg from it are cool.
2001 Laser Red GT convertible; all of the usual bolt-ons.
1967 Notch; 200 I-6, C4 auto.