Antitheft Alarm -(ATA) System Description
85mercedes01TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: January, 1985 REF. NO. MBNA 82/16
SUBJECT: ANTI-THEFT ALARM - MODEL YEAR 1985
W/C 123 Models
This system continues unchanged from model year 1984. Information regarding this system is contained in S.I. MBNA 82/11, April 1984.
W/C 126 Models
Several changes were made to the system for model year 1985. Refer to the service microfiche, "Electrical System, Model 126, Groups 15, 54, 82" (8/84) for details of the revised operation and electrical schematics. The additional double-fuse holder which is mentioned in the microfiche schematic is located on the left front wheel housing.
In case of complaints regarding the alarm system becoming activated on its own (without any outside disturbance), the most frequent cause has been found to be a defective anti-towing sensor. This can be checked by unplugging the connection to this sensor and observing whether or not the failure still exists.
NOTE: The rest of the alarm system is still functional when the sensor is disconnected.
Troubleshooting Hint:
There is a difference between an arming/disarming failure and an activation failure. If there is an arming/disarming failure (e.g. alarm system becomes activated after unlocking and opening door), then only the arming/disarming section of the system should be checked. This would include door handles (and trunk lock on 1985 models) and related wiring. If there is an activation failure (e.g. alarm system starts sounding on its own) then only this section of the system should be checked. This would include any sensor which would activate the alarm system such as pin switches, brake light signal, anti-towing sensor, etc.