Thanks. I've debated trying ForScan, but I believe it only with with Windows, right? I don't currently have that at home. I need to figure that part out, but I might just have to resort to a VM or something on a Linux box.
I think I could have more clearly communicated what I was saying. So yes, there's always a voltage on one of the harness pins, because it's tied to a hot wire. But the other harness pin (#2) is connected to the TCCM, which should toggle that pin between Hi-Z ("open") and closed, the latter of which would complete the circuit. Am I understanding this correctly?
But my problem is that pin #2 is always grounded no matter what. I'll look into this deeper after work - probably gonna see if there's continuity between ground and the pin when the truck is on, off, on with the 2H setting, on with the 4L/H setting, etc.