[tsubaki]

The green wire is the right blinker and brake light.
The yellow wire is the left blinker and brake light.
The brown wire is the running lights.
The white wire is the ground.
The fact that it works on the Tahoe was a quick analysis (good job), check and see if you get a reading between the white wire and the brown wire (with parking lights on) with a test light (not a meter) closer to the harness away from the plug to see if the plug is damaged.
The fact that the truck had wires spliced could be the whole problem also. I had one that the lights would occasionally not work until I got under the truck and wrapped my hand around the wire connections and twisted.