ok now we get to the fun part
behind the taillamp there should be a connector this connector should have 7 wires, we only want to focus on the gray wire right now, you will want to disconnect that connector
once its disconnected put the meter to ohms, the black lead onto the gray wire at the taillight and the red onto pin c or the third one in the row of 4, if you look on the back side you should see the gray wire. we want to test the wire from the connector to the taillight