This 1997 Chevrolet K1500 Pickup came in with the complaint of the left turn signal will not work with the headlights on. I checked and the turn signals did work with the headlight off but the actual problem was that the turn signal would not work with the park lights. In fact if the park lights were turned on the left turn signal indicator light in the dash would come on and stay on. From experience I thought the problem would be in the left front light assembly and possibly a bad ground or a shorted bulb. I removed the screws that held the light in place.
Then I removed the sockets from the light assembly. The bulbs looked okay but I went ahead and pulled the bulbs out. The bulbs were not damaged. But I did see something strange in one of the sockets.
It was the solder from an old bulb that had come out and gotten stuck between the two terminals in the socket creating a short between the park and turn signal light circuits. Another one fixed.
had big problems with turn signals and parking lights interactions.
resolved it when i saw the corrosion on the trailer connection. cut it off and the lights all work again.