[nikwho]

Headlight switch sounds suspect right off the bat. If there are only two leads to the lights (one for parking lights, the other for stop/turn), then like you said, you know that the led's work. And, you know that the wire running from cab to light is good. I had similar problem with my '59. LED lights, Rebel Wire harness. I had brake lights that functioned, AND rear turn signals worked fine, but with EITHER R or L turn signal, both front blinkers would blink. Drove me nuts. Finally just replaced my turn signal switch, which was already brand new, and that finally fixed my issue.

Anyway, I'd look very closely at your headlight switch, as the power for all of these lights run through that switch. Secondly, I'd make certain that I was 100% certain that the turn signal switch was functioning correctly.