Active Lsd R33 Gtr Vspec Problem

[viking]

i hav a r33 gtr vspec. the a-lsd light in the dash lights up which in turn only runs rear wheel drive. the ecu in the boot flashes once and five times indicating front right speed sensor, of which i hav replaced but problem still exsists. i hav checked the green 30amp abs fuse in the boot which was blown. replaced it then it blew straight away. i figured it may be a circuit problem. does anybody know how to isolate where the circuit problem may be or how to run other checks. has anyone had this problem??