R129 - Alarm/immobiliser issue

[Rud]

I had a problem with the alarm on my R129 last week. Had to bring the car to the stealership to get it fixed. Turned out it was a vacuum component causing the problem.
The stealership first claimed it was a problem with the unoriginal immobiliser I installed last year, but no, as stated a vacuum part with the original alarm.

The stealership told me that the alarm already had immobiliser functions, so why the additional one …? When I bought the car there was another 3’party immobiliser and since this didn’t work, I just assumed there wasn’t any in the first place and installed one. But, one thing the stealership couldn’t tell me was what type of alarm I have and to what extend the immobiliser works, if it only disconnect the starter or the more advanced ones, disconnect the fuel pump and other vital parts to make the car start.

Can anyone help me, by telling me where to look or, if they know the type of alarm installed in a 1993 R129 500SL.

Rud