If I had to guess - (depending on the year of the truck) it's probably
the multi-function switch in the column has gone bad. It controls many
things in the truck, cruise, flashers, wipers, brake lights, turn
signals, etc. I just replaced mine because my brake lights and hazard
flashers stopped working. The dealership wants close to $400 for the
switch, but it's commonly available from many other places so shop
around. I bought one new for $165.