My speedometer and brake lights quit working in my 92 Peterbilt 379.?

My trucks brake lights and speedometer does not work. The truck was parked for about six weeks and not started. I noticed the speedometer was not working and a friend told me the brake lights were out. Everything else seems to be working. Are these items fused? Can the problem be related or serperate? I am not a truck mechanic, I only drive it. Any help would be appreciated. Thanks!|||check fuses first...then go from there...till you find current follow circuits back from problem