I think there may be a 3 pin plug which controls part of the ignition / injection sytem...I don't have access to an ST4 wiring diagram, but the 996 one I have has it on that diagram as feeding the injector relays
This is a logical location for another circuit break to immobilise the bike.
Do you have the wiring diagram inthe back of your hand book?
If so, it shows the number of contacts in each plug inthe loom & you may be able to deduce the poisition it plugs into fromthat.
Failing that, give Nelly a ring tomorrow..