Welcome to the forum.
Have you looked around the brake pedal on top of arm of brake pedal you may see a switch with a plunger that drops down when you depress the brake pad.
Have you ever checked behind the brake lens and checked the wiring and lamp sockets on a metal bar with ground wiring and power wiring to lamps.
Everything may need to be cleaned up from corrosion on wiring and bar for lights. --Brochure
--- Owners Guide
1997 Oldest we have.
has some older coach information and all links below in my signature will have info for your Newmar.