Security system – assuming it is purely for your lot, then it is the owner’s responsibility. Doesn’t matter when it was installed.
Electrical fault – depends on where the fault is. If the fault is in your fuse box or your lot’s wiring, then it’s your responsibility. If it’s between the “common meter box” and your fuse box, then it’s the OC’s responsibility. I guess you don’t exactly know where the fault is. Discuss with the SM – if they are not prepared to engage an electrician to repair the fault, organise one yourself, and get the SM to confirm that the OC will reimburse your costs if the fault is found to be outside your lot.
Note – I’m in NSW, not sure how things work elsewhere. I’ve found this document helpful in resolving these types of issues.