99 turn signal problem, very strange

This is strange,

then about a week later. Left turn signal will not blink when the head lights are off. While the head lights are off and the turn signal is in the left turn position , a press of the break pedal causes all the dash lights to dim. When the truck is shut off WHILE the break is depressed the head light warning light sounds until you take your foot off the break. and sounds as soon as you depress the pedal again. The right signal is working fine.

with head lights on the signal works.

My mechanic can not figure it out and say to take it to the dealer.

all the obvious have been checked. ect... bulbs, wires.

does this sound familiar with anyone?

any help would be greatly appreciated.

Dan