Antitheft Alarm - (ATA) System Description and Wiring
84mercedes03TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: April, 1984 REF. NO. MBNA 82/11
SUBJECT: A. ANTI-THEFT ALARM SYSTEM MODEL 126
B. ANTI-THEFT ALARM SYSTEM WIRING DIAGRAMS MODELS 123 (EXCEPT 123.193) AND 126
A. Anti-Theft Alarm System Model 126
As of model year 1984, a factory-installed anti-theft alarm system is standard equipment on all 126 models.
This system incorporates switches as part of both the driver's and passenger's door handle assemblies. Arming or disarming of the system is accomplished via these switches. It should be noted, however, that only the master key will arm/disarm the system in the 126 models.
System will not Disarm
In cases where the alarm system cannot be disarmed by unlocking either door handle, and the alarm is activated by opening the door, both front door handles should be replaced.
NOTE: Door handles of an improved design have been installed in production as of February 23, 1984 (chassis end no. 056313). The microswitch for the alarm system now offers greater resistance to water entry, and a previous opening in the lock assembly casting has been closed.
If the ATA does not disarm the following procedure should be used while waiting for replacement parts:
1. Attempt to disarm the system by unlocking the passenger door lock with the master key; in most cases the driver's and passenger door switches will not malfunction at the same time. If this is successful, the auxiliary trunk lock of the alarm system will be moved to its unlocked position and will remain in this position after the control unit for the alarm system is disconnected.
2. If unlocking the passenger door lock does not disarm the system, the control unit should be disconnected. On 126 models the unit is located in the passenger-side foot well area, under the floor mat (Service Microfiche incorrectly indicates driver's side).
3. When the alarm system has been disarmed by disconnecting the control unit, the truck will remain locked by the auxiliary trunk lock. Each time access to the trunk is required, it will be necessary to simultaneously pull the emergency trunk release cable (left side of car, under rear seat cushion) and push the trunk lock button in (two man operation).
4. The auxiliary trunk lock can be permanently switched to the unlocked position (with the control unit disconnected) by momentarily jumping pin socket no. 4 to pin socket no. 1 (ground) of the 14-pin connector to the control unit. The trunk lock will then move to its unlocked position and stay there until the alarm system is repaired and reconnected.
IMPORTANT: If absolutely necessary, the ATA can be disarmed by removing fuse no.
15. However, this is not recommended because other systems (e.g. courtesy lights, radio, antenna, seatbelt extender, etc.) will then be inoperative. In addition, the above solution for electrically switching the auxiliary trunk lock to its unlocked position will not work because power will be removed from the trunk lock.
Parts Information
Model Part Name Part Number
126.032/.037/.120 Door handle, left 126 760 27 59
Door handle, right 126 760 28 59
126.044 Door handle, left 126 760 33 59
Door handle, right 126 760 34 59
NOTE: It is very important to be absolutely certain that the correct key code is stated on the parts order form to insure the minimum waiting time for new parts.
B. Anti-Theft Alarm System Wiring Diagrams Models 123 (Except 123.193) and 126
Operating characteristics and wiring diagrams can be found in group 82 of the Service Microfiche. A revised microfiche will be issued in the near future which incorporates two modifications:
1. The wiring for the anti-towing sensor (standard on 126 models as of January 1984 production/not available on 123 models) will be included.
2. The location of the anti-theft alarm control unit for the 126 models is incorrectly indicated in the existing microfiche. The correct location is under the front passenger footrest area.
For your convenience, the attached wiring diagrams can be used until the microfiche is revised.
Wiring Diagram-Anti-Theft Alarm System Model 123.153 (300 CD)
Wiring Diagram - Anti-Theft Alarm System
Model 126 (Except 126.044)
Wiring Diagram-Anti-Theft Alarm System Model 126.044 (500 SEC)