Alarm wiring 92 UK car

[abovetherim]

Hi folks

New member here with a recently purchased 92 uk market silver/black car

It has a few issues that I have to tackle so I have been reading threads to the early hours.

The car has had door lock holes smoothed over and relies on key fob to lock/unlock. For this it has had an after market alarm installed but only the feature for the central locking. I have yet to dig in and assess the wiring etc.
It also seems to have had another alarm fitted to it previous to that as there is a siren in the engine bay.

I found a thread on installing alarm using the security harness located in the boot (trunk) area. Now my car does not have a security LED in the dash so would I be right in assuming that it never had an alarm from factory and would not have the loom and plug in the boot?

If it should be there will it be under the shelf or in the wings?

Thanks
Jan