Okay, 91 Toyota pickup

This is a long shot...

Rear brake lights don't work (running lights or brake lights)
License plate lights don't work
Cluster illumination doesn't work

Cluster illumination, license plate lights, and rear running lights should all work off the turn signal switch (turning your headlights on)

Any idea? I don't know where to start...

 

fuse ?

 

Check your fuses, make sure there not corroded, check the fuses with a meter, sometimes they can look good but be bad.