Leaderboard

Good job And probably needed the battery anyway

I would use the existing wiring as a base for a hybrid system myself. Too many times have I seen old systems ripped out and junk replacing it. Yes some of the tatty wiring maybe removed but if the system was in good order at some point it may reduce installation or service costs to reuse some of it. For the more direct questions, yes the alarm is likely to sound if you tamper with it. There is no guarantee that any service/engineer modes would work so expect it to rattle your ears. They're designed to be hard to disable and bring attention to the fact someone is tampering with it, if installed and serviced correctly.