Kjmaupin Standard transmissions do not have a brake light switch under the dash. It is on the brake booster under the hood. I would disconnect the electrical connector on the booster and check the switch for continuity. If it is stuck closed then that would be the first thing to replace. Some info says the switch itself is integral to the brake booster and can not be replaced separately. (You must replace the booster and the switch) . I DO NOT KNOW THAT TO BE A FACT. I would think the brake light switch could be replaced by itself. I just do not know as the standard transmission cars are different than anything I own.

Wiring is also different than the automatic trans cars.

The relay for the brakes is in the under hood fuse box near the brake booster. Take off the lid you see two rows of fuses. You must lift that top layer of fuses as the relay you are looking for is under that top layer. You must use a screw driver to pry the tabs loose from the sides and then pull up on that top layer of fuses to get down below. Once under there the relays are up against the back (firewall side) of the fuse box and the brake relay is the one closest to the center of the car. Good Luck!

PS If the brake light switch is at fault your cruise control should not be working. As you know when driving with cruise control and you put on the brake the cruise control disengages. SO if cruise control is working normally I would suspect you have a ground problem in the wiring and not a switch problem. You may need to start at the brake socket in the rear of the car, inspect that completely, and work your way back through that wires