danewguy,
First off, in just about any electrical test with a test light, always make sure that the ground that you're clipping the ground to is a good, clean ground. I've done that more times than I care to admit. Testing, testing and testing and no light. Come to find out, the ground I was on was not a good ground. Also, I ALWAYS test the light, right on the battery terminals to make sure the light is functioning fine. Nothing like trying to find a fault with faulty testing equipment.
So, once that's established, then yes, a test light should reveal the function of each of the pins. I always start out with the running lights. It's just a preference, there's no real pattern. I also draw a picture and label each pin for function.
Now, if you're not getting power at every one of those pins, then one, it's possible that the back side, where all the wires enter the pins could all be corroded, not likely but, possible.
Second, there's another plug/connector some place in the wiring that connects that harness to the main harness of the coach/fuse connections. Now, you say you've found the fuses for the trailer plug and they "appear" to be OK? You can use your test light on them too. Just make sure you've got a good ground and then touch the exposed metal part of both sides of each of those fuses. Sometimes, the fuses may make a bad contact and or, are broke internally and they appear good but, in fact, are not.
Now, once you've determined the fuses are good, then you'll have to start tracing those output wires, and possibly "probing" them once in a while to see if you've still got power. You'll do this all the way to the trailer plug on the back. Hope this helps some.
Scott
