Thought these diagrams might help.....I colored in red where the short to ground could be....as you can see the lock relay is already in the ground position, so when the unlock relay is energized, it's contact switches position and provides power to the circuit from the right side of the solenoids.....it doesn't matter that the left side of the circuit(in red) is shorted to ground, because that side is suppose to be grounded by the lock relay.....However, when the Lock relay is energized, the lock relay contact moves to power, and the first thing that power sees is a short to ground(red circuit) and blows the fuse....
This is why I say diagnosis begins at the fused block.....you disconnect C4, and with an ohm meter attached to ground, or, a test light attached to BAT, you probe circuits "L" and "K" in the harness.......this will tell you which circuit is shorted.....unfortunately if it is K, it could be either circuit going to either door actuator, and gets a little more involved in testing....
