Thanks for the help, especially the wiring diagram.
To fix my problem, I did the following:
On the brake fluid reservoir, there are 3 wires going to 2 connectors. Identify the single wire and trace it through the firewall.
On the back of the instrument panel, there is a round connector with 12 pins. The wire from the reservoir goes to pin #5.
I cut this wire and soldered in a new wire running to the parking brake switch. I cut the wire in a place where I could solder easily.
Now, either the parking brake or a low brake fluid situation will trigger the “BRAKE” light to illuminate.
I hope this helps anyone else with a similar problem.