Truck Repair: brake lights, turn signal switch, chev blazer

Question
We have a 1995 Chev Blazer and the brake lights are not working.  The third brake light will light but that is all.  We have tail lights, turn signals and headlights.  We have replaced the brake switch under the brake pedal but still nothing.  The fuses under the dash are fine.  We are being told that there might be another fuse box in the engine department.  Is this true and if so where is it located.  I might mention that we have wiring to haul a cargo trailer and the brake lights on that are also not working.  Please help us with this problem.  Thank You
Tracey

Answer
Do some wiggling of the turn signal switch, and the emergency flasher switch, and if that doesn't do it, the flasher may need to be replaced.
I assume the lights on the trailer did work correctly before.
But get them working with the trailer unhooked first.
Van