What is with this alarm system.....?

[Gmach]

I can't figure out the alarm system on this 92 400E. Every time I close the trunk it locks ALL the doors.
Also, if I use the trunk lock to unlock the car then open the drivers door the alarm goes off. I have to lock/unlock the car with the trunk to turn it off! What is going on here?

 

[autoworrks]

it's a 22 year old alarm system that has gone quirky. I had a similar situation on my 92 Diesel so I disconnected the system.

 

[Klink]

I can't figure out the alarm system on this 92 400E. Every time I close the trunk it locks ALL the doors.
Also, if I use the trunk lock to unlock the car then open the drivers door the alarm goes off. I have to lock/unlock the car with the trunk to turn it off! What is going on here?

The switch inside the pneumatic element for the trunk lock, and/or it's connected wiring is almost always the cause of a problem like this. Unlike the doors which use micro switches for alarm control, the alarm arm/disarm signal via the trunk is a read directly from the power lock switch in the trunk lock pneumatic element. It sounds like that switch has probably come apart and / or failed in such a manner that with a little bit of disturbance your door locks are being activated, and if the alarm control units sees the signal from the trunk actuator switch before any of the other pneumatic actuator switches are displaced, the alarm control unit "assumes" that someone with a master key has rotated the tumbler in the latch, and it arms or disarms the alarm accordingly.

Moisture in any of the trunk latch related stuff in the rear wall below the trunk lid can give you similar malfunctions.

Also, check for moisture under the rear seat cushion, both on the left side and on the right side. Moisture in the left side can attack related wiring and the control unit for the convenience closing feature. Note that these circuits have direct tie-ins to microswitches in the front doors and on the trunk latch. Moisture in the right side floor can directly attack the pneumatic pump and it's related wiring which also has some commonality with the ATA system and the convenience closing systems.

Best!

 

[Gmach]

Thanks...I'll pull the lock out of the trunk. No moisture issues. I've seen this happen in another 400E

 

[Gmach]

....so how do we COMPLETELY disengage (unplug) the alarm system...? Does unplugging thje red connector under the passenger floor mat do it..COMPLETELY?

 

[gsxr]

....so how do we COMPLETELY disengage (unplug) the alarm system...? Does unplugging thje red connector under the passenger floor mat do it..COMPLETELY?

No, the red connector is for the SRS (airbag and belt retractors). Make sure you don't unplug that one.

The "Becker" box near the red connector is the alarm brain. Disconnect that and your alarm issues should go away on your 1992 model. I don't believe additional measures are necessary except for 1993-1995 models, which have the little LED blinker on the HVAC panel, and a starter-disable relay that must be bypassed. Yours should be un-plug and play.

 

[gerryvz]

Be sure that you disconnect BOTH connectors from the Becker box under the passenger floor panel.

 

[Klink]

No, the red connector is for the SRS (airbag and belt retractors).

The "Becker" box near the red connector is the alarm brain. Disconnect that and your alarm issues should go away on your 1992 model. I don't believe additional measures are necessary except for 1993-1995 models, which have the little LED blinker on the HVAC panel, and a starter-disable relay that must be bypassed. Yours should be un-plug and play.

Be sure that you disconnect BOTH connectors from the Becker box under the passenger floor panel.

That will get the job done. No extra measures will be needed unless it is MY 1993 or newer.

 

[visal911]

That's correct,

On the 94-95 ones with the immobilizer all you have to do is unplug the connector and bridge ports 1 and 2 on the bigger connector and that will by pass the Immobilizer. No need to tool around taking apart the cluster, etc.