Turn signal short? F250 1987

everything needs a ground , you need a multi tester to see what has power/ground and what don't

Still sounds like a grounding issue. There are grounding points all over this truck, in the front, in the rear, battery to engine, engine to frame, frame to body. On my old Ford truck I ran some ground straps from frame to body.

I just remembered something I ran into back in the day, to make it short, check the 4 way switch, it might not be fully seated in the off position causing a feedback or loss of proper current, cycle it a few times and make sure it works as it should. Then check everything.

I found the fix to be with the driver side rear tail light bulb. It had an internal short across the running lights and turn signal brake lights circuits. It produced approximately 5 volts of power feeding into the running lights circuit causing the flasher relay circuit to safety and putting low voltage into the illuminated dash running lights. Creating a closed low voltage circuit between signals and running lights produced questionable circuitry wiring schematics as they are both independent circuits until a bulb has internal voltage bridging. Independent circuits are always dedicated circuits until introduce to a light bulb. Simple fix confusing diagnosis. Thanks for all your feedback. Scooter