Toyota Repair: electrical problem, power brakes, toyota pickup

Question
have 1991 toyota pickup with 90000 miles a/c power brakes 5 speed trans 2.2r engine i have problems when i try to turn headlights on they come on but dash lights and rear running lights don't they will come on but you never know when also seems like it does it more in warmer times of year not any problems in winter

Answer
The dash illumination and the tailights are on the same circuit and share the same fuse.
Does the truck have a traier hitch and if so is it factory or aftermarket installed.
The problem could be in the towing harness converter and you may have to replace the towing harness complete with the converter.