[RustyPile]

Here's a test you might try.. Buy a new dual contact bulb socket for an 1157 bulb, along with an alligator clip large enough to grip around the socket.. Attach a wire to the alligator clip and wire up the socket to the harness using jumper wires.. Attach a wire to the big alligator clip and use it to ground the socket. Be sure the socket is well grounded and run the turn signals through their paces.. If the bulb in the test socket blinks as it should, you'll know for sure the socket on the truck is bad..