Should be a "relatively" easy case of tracing all the wires. I'm sure most installers do not go to excessive lengths to hide splices etc
Although it would still be a PITA to do with wiring access etc.
Is a unit faulty or something ? Can you find out what model it is and get wiring diagrams for it ? Might be handy if instaling a new alarm.
Sigma where dealer fitted, badly. The unit is wired into fuel pump/starter/indicators
You can find the unit itself tucked up behind the steering column
The wiring used is thin gauge compared to likes the fuel pump wiring its spliced into leading to it burning out the relay in the immobiliser unit.
Happened on my my99 uk turbo and was able to bridge the fuel pump immobiliser wiring and immobilise it just on starter