Alarm System - Tester Adapter Harness
REF. NO. 58/80TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: April 1995
SUBJECT:
MODELS 124 AND 201 WITH ANTI-THEFT ALARM (ATA) AS OF M.Y. 1993 ADAPTER HARNESS FOR MB ALARM SYSTEM TESTER
The MB alarm system tester detects and stores signals to indicate which anti-theft alarm (ATA) sensor caused the ATA to activate. It is designed to store an ATA sensor activation only when the ATA is armed, as indicated by a ground signal at pin 1 of the 14-pole connector on the ATA control module (N26). Pin 1 of the 14-pole connector is open-circuited when the ATA is disarmed. This function applies to 124, 201, 126, and 107 model vehicles equipped with ATA up to model year 1993.
As of model year 1993, the function of pin 1 was inverted: As a result, pin 1 is grounded when the ATA is disarmed and is open-circuited when the ATA is armed. This is used to control the starter lock-out relay module (K38). Due to the above mentioned functional change, the MB alarm system tester stores sensor activations only when the alarm system is disarmed, and therefore is not effective in diagnosing ATA system complaints.
The MB alarm system tester can, however, be modified to allow testing of both versions through the use of a shop-made adapter harness. The adapter harness consists of an extension harness, a relay module harness which uses a SPDT relay module, and a DPDT switch to switch between the two types of ATA systems. Instructions for fabricating the adapter harness follows.
Fabricating relay and extension wiring adapter harness
IMPORTANT!
Select 18 gauge wire to fabricate the wiring harnesses.
The circled numbers in Figures 1 and 2 indicate each individual wire and/or solder location.
Fabricate both relay and extension harness using Figures 1 and 2 as a reference.
Fabricating relay module harness
1. Carefully assemble the 4-pole plug with pins, using the following parts: 4-pole plug, part number 009 545 5228, 4-pole plug part number, 009 545 2128 and 4-pole pin, part number 001 545 3826, as noted in the Parts Information.
2. Using 18 gauge wire, cut 9 lengths of wire to approx. 6 inches each.
3. Starting on one end of the wires, solder wire ends as noted by circled numbers, to the appropriate pole locations of the SPDT relay module socket (part number 011 545 5028). Cover wires with the appropriate size plastic tubing as harness is being fabricated, see Figure 2. Continue by soldering wires to the DPDT toggle switch and previously assembled 4-pole plug with pins (Figure 2). Cover wires as before with plastic tubing.
4. Cut a short length of 18 gauge wire, for use as a jumper wire on the DPDT switch. Carefully solder jumper wire (wire 11, Figure 1) to the terminals (11) of the DPDT switch.
Fabricating extension harness
1. Use 18 gauge wire, cut 4 lengths of wire to approx. 10 inches each.
2. Solder one end of the loose wires to the appropriate pole locations of the 4-pole socket body (part number 007 545 0028) (Figure 2).
3. Cover wires with the appropriate size plastic tubing.
Note:
The loose wire ends of the other end of the extension harness will be soldered to the 14-pole connector of the MB alarm system tester.
Soldering extension harness to 14-pole connector of the MB alarm system tester
1. Carefully open the 14-pole connector of the MB alarm system tester.
2. Unsolder the tester wire from the plug-socket in position 1 of the 14-pole connector (Figure 1).
3. Solder the free end of wire 4 of the previously fabricated extension harness to the tester wire just removed from position 1 (arrow, Figure 1).
4. Insulate the solder connection (arrow, Figure 1) of the tester wire and wire 4 of the extension harness with heat shrink tubing.
5. Solder the free end of wire 2 of the extension harness to the plug-socket in position 2 (Figure 1).
6. Solder the free end of wire 3 of the extension harness to the plug-socket in position 3 (Figure 1).
7. Solder the free end of wire 1 of the extension harness to the now empty pole socket (see Step 2) in position 1 (Figure 1).
Note:
In adding wires 1 - 3 to the 14-pole connector, make sure existing wires at individual plug-sockets are not damaged, disconnected, desoldered, etc.
8. Carefully close the 14-pole connector without pinching any of the wires.
9. Insert the SPDT relay module (part number 001 542 0219) into the SPDT relay module socket (part number 011 545 5028) of the relay module harness (Figure 2).
10. Connect the 4-pole plug with pins and 4-pole socket body of both harnesses together (Figure 2).
Testing the fabricated adapter harness
! IMPORTANT!
Before connecting the MB alarm system tester with the fabricated adapter harness to a vehicle, please be certain to check each connection with an ohmmeter for short and open circuits.
1. Make two labels, "--> MY 92" and "MY 93 -->", these labels will be taped to the DPDT toggle switch in step 4 below, as necessary.
2. Choose one of the following:
^ If a M.Y. 1993 or later model 124 or 201 vehicle (with ATA) is available for testing, proceed to step 3A.
^ If a M.Y. 1992 or earlier model 124, 126, or 201 vehicle (with ATA) is available for testing, proceed to step 3B.
3A. With the tester installed in a M.Y. 1993 or later vehicle (model 124 or 201), lower the front windows. With the vehicle unlocked and the ATA disarmed, press the RESET button on the tester. Then open any door.
^ If the indicator lamp illuminates on the tester for the door opened, then the DPDT toggle switch is in the "--> MY 92" position.
^ If no indicator light illuminates, repeat the test with the DPDT toggle switch in the other position.
3B. With the tester installed in a M.Y. 1992 or earlier vehicle (model 124, 126 or 201), lower the front windows. With the vehicle unlocked and the ATA disarmed, press the RESET button on the tester. Then open any door.
^ If the indicator lamp illuminates on the tester for the door opened, then the DPDT toggle switch is in the "MY 93 -->" position.
^ If no indicator lamp illuminates, repeat the test with the DPDT toggle switch in the other position.
4. Once either the "--> MY 92" or the "MY 93 -->" position have been determined via testing, mark the DPDT toggle switch accordingly with both labels.
Parts Information