[Gardtec 370 door sensor]

Have a Gardtec 370 alarm that was here when we moved in. Suddenly the door sensor has stopped working. Managed to buy a new one but links and connections look different. If I connect as it says with the links it says it does not wwork. Will work if I remove the alarm link but only as a door chime. Anyone know how many wires go to the door sensor? Maybe I forgot somethhing. (Not unusual lol.)