Diagnosing a short circuit is not easily described here, but I can try.
Somewhere in the circuit that is blowing the fuse there is a hot (positive) wire that is shorting out to ground. This can be a wire rubbing on a piece of metal, or a faulty component like a bad lock motor.
The way I start with this type of problem is to start by visually inspecting any wires that may be visible, looking to see if any are rubbing on a bracket or sharp edges.
Then start disconnecting components in that circuit until the fuse stops blowing, and if that doesn't work, start eliminating sections of the circuit by disconnecting wires.
Once you've isolated the part or part of the circuit that is causing the short, then find it and fix it.
Sounds easy, but these are generally very difficult to fix. Good Luck