If it is the alarm system horn going honk, honk.
Use the key in a mechanical door lock to LOCK then UNLOCK, and hope it dis-arms.
FYI: This alarm module is a vehicle disabler security item and has been superseded NINE times. Note: Any replacement alarm module MUST be ordered by VIN# and coded with the MB factory tool.
The alarm module is in the passenger rear quarter panel, shaped like a large capitol "L".


If it is the standard vehicle horn on continuous blast.
#1. Disconnect the battery.
#2. Open the hood.
#3. Remove the primary fuse panel cover.
#4. Remove the Secondary fuse panel cover.
#5. Connect the battery.
#6. Remove the (ice cube size) relays one at a time until the trumpet horn goes off.

Relay
MB# 0015429919

#7. Install the Secondary and primary fuse panel cover.
#8. Replace the defective relay at your leisure.


Data for you.
Locate the pair of horns under the front bumper, and disconnect both of them.
FYI: The horns have been superseded three times each.

Horn, 405 Hertz tone
MB# 0045424120

Horn, 485 Hertz tone
MB# 0045424020



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__________________
ASE Master Mechanic

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D

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