Cliffordingles did a new switch fix your problem? I'm having same issue. Front left turn signal does not work (dash or light). Rear left signal works correctly all the time. However both front and rear lights (and dash) work correctly when I turn my flashers on.

I got the truck and was having issues with lights and replaced the turn signal flasher. Then realized it was actually the turn signal switch not returning back to neutral completely causing my issues so I replaced turn signal switch and key switch while it was apart (it did not require key to start) at the same time. When I first replaced the key switch it wasn't popping back to "run" from "start" 100% of the time and caused all signal lights not to function. That has corrected itself, the new key switch kicks back to "run" position every time now and no more signal issues... I thought.

I realized my front left wasn't working (almost wreck). I just thought my dash light was out. Trailer turn signals all work as well. Anyone have any ideas? I can't understand how rear lights function front do not unless they run 2 different wires from switch to relay. 83 F-250 6cyl 4 spd 4x4 reg. cab long bed -NO TILT. Thanks Cory

 

Check your bulb sockets. I had a corroded one up front years ago and it caused all sorts of crazy problems. Sometimes it'd stay on, other times it wouldn't come on...it's weird.