brake light sensor

[Jesse van Herk <vanherk@domain.elided>]

>My guess is the wire you found is the "BRAKE" dummy/idiot light on the 
>dash.. BUT, on a truck that old, I don't know for sure.  Typically it's 
>there to sense a difference in brake pressure = brake system
leak/failure.
>- -Tom

so you're saying there are no brake lights on the truck? I'll have
the exact same problem when I get everything else finished. 
  Would that little pressure sensor act some kind of rheostat?(more
pressure, more lights going on???)  Somebody must know.
-Jesse vH