[patrickt]

Dan, if you disconnect your trailer relay on the 3-wire "car side," and then turn the car on, and touch the brakes, the RED wire should have a 12v continuous. Take your foot off the brake and put on the left turn signal. The front left light bulb should be flashing and you should get a pulsing 12v at the YELLOW wire. Put the right turn signal on and the right front bulb should now be flashing and you should get a pulsing 12v at the GREEN wire. If this doesn't happen, then there is a problem upstream from your trailer relay -- either a wiring fault or the turn signal switch is bad, or maybe something else. But that's your first diagnostic test. If you can't pass this test, then there's no point in actually removing the trailer relay.