Hello,

Today when I was driving with my 1989 F-350 (only 8000 miles)
I lit the lights, when I came back home I was checking things in the barn, truck was running Idle with lights on, and all lights with the exeption from the headlights stopped burning,...
I have no idea where to look for? (the fuse wasn't blown)

 

bump , still didn't found it?

 

Turn signals and brake lights too?

 

My trucks a 95, but I had a similar problem. I thought it was the headlight switch, so I changed it out and had the same problem. My issue turned out to be a fuse, so maybe look there

 

It's a bit ago in the mean time, but yes I thought the brake light as wel, blinkers I didn't try.

It seemed to be a fuse, but the strange thing is that after replacing the fuse my external marker lights (aftermarked obligitory here) didn't come back on???

 

check the plug going into the headlight switch closely for burn marks or melted look. .
they get hot and start to melt. when this happens you will loose the lights.
fix is a new headlight switch and plug harness. price here in the states is around $35 for both. so figure $50-60 over there.