Trailer Turn Signals Not Working When Headlights Are On. But when always on lights your headlights are turned on the total current draw may be more than can be passed by the harness due to the weak ground connection. Be sure that whenever your lamp is grounded you have a good known chassis ground. Check the fuse on the powered converter to ensure it is still functional.
Then use a circuit tester like 40376 if you do not already have one to test the connector on the truck. First check the trailer wiring harness on your tow vehicle with a circuit tester like part 40376 and make sure all of the functions are working correctly without the trailer connected. It s very possible that a weak ground connection can be just strong enough to allow sufficient current for some lights to pass but not enough for everything. It worked just 3 or 4 days ago.
Be sure that whenever your lamp is grounded you have a good known chassis ground.
Once the lights are turned off everything will work fine again. Then use a circuit tester like 40376 if you do not already have one to test the connector on the truck. The reason the turn signals quit working when the lights are on is that a 12 volt signal is now being sent down the opposite wire which was acting as a ground before. However when i turn on the headlights or parking lights the right signal ceases to function. First check the trailer wiring harness on your tow vehicle with a circuit tester like part 40376 and make sure all of the functions are working correctly without the trailer connected.